Ethylene receptor biosensor

Abstract

The present disclosure relates to biosensors (10) having a receptor layer (5) and a mediator layer (6), the receptor layer including ethylene receptor molecules. The present disclosure also relates to sensor units (20) comprising one or more biosensors (10) and a controller (11). In some embodiments, one or more sensor units (20) may be in wireless communication with a receiver module or a network gateway.

Claims

1. A biosensor comprising: (a) a reference electrode comprising (i) a mediator layer deposited on a base electrode; and (ii) a protein receptor layer deposited on the mediator layer, wherein the protein receptor layer comprises an ethylene receptor protein; and (b) a counter electrode in communication with the reference electrode.

2. The biosensor of claim 1, wherein the base electrode comprises a material selected from the group consisting of copper and silver.

3. The biosensor of claim 1, wherein the ethylene receptor protein comprises a nucleotide sequence having at least 90% sequence identity to a wild-type polynucleotide sequence of an ethylene receptor gene.

4. The biosensor of claim 1, wherein the ethylene receptor protein comprises a nucleotide sequence having at least 95% sequence identity to a wild-type polynucleotide sequence of an ethylene receptor gene.

5. The biosensor of claim 1, wherein the ethylene receptor protein is derived from Zea mays.

6. The biosensor of claim 1, wherein the ethylene receptor protein is derived from Arabidopsis.

7. The biosensor of claim 1, wherein the ethylene receptor protein comprises an amino acid sequence having at least 90% identity to any one of SEQ ID NOS: 1, 2, 3, and 4.

8. The biosensor of claim 1, wherein the protein receptor layer comprises between about 10 to about 1000 nanograms of ethylene receptor protein.

9. The biosensor of claim 1, wherein the mediator layer comprises at least one of potassium ferricyanide, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium chloride, naphthol green, or polypyrrole.

10. The biosensor of claim 1, further comprising a working electrode.

11. A sensor unit comprising a biosensor and a controller in communication with the biosensor, wherein the biosensor comprises: (a) a reference electrode comprising (i) a mediator layer deposited on a base electrode; and (ii) a protein receptor layer deposited on the mediator layer, wherein the protein receptor layer comprises an ethylene receptor protein; (b) a counter electrode in communication with the reference electrode.

12. The sensor unit of claim 11, wherein the controller comprises a communication module.

13. The sensor unit of claim 11, wherein the communication module is a wireless communication module.

14. A biosensor consisting essentially of: (a) a reference electrode comprising (i) a mediator layer deposited on a base electrode; and (ii) a receptor layer deposited on the mediator layer, wherein the receptor layer comprises an ethylene receptor; (b) a counter electrode in communication with the reference electrode; and (c) a working electrode.

15. The biosensor of claim 14, wherein the ethylene receptor protein comprises any one of SEQ ID NOS: 1, 2, 3, and 4.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For a general understanding of the features of the disclosure, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements.

(2) FIG. 1 illustrates a top down view of a biosensor in accordance with one embodiment of the present disclosure.

(3) FIG. 2A illustrates a side view of a reference electrode in accordance with one embodiment of the present disclosure.

(4) FIG. 2B illustrates a side view of a biosensor in accordance with another embodiment of the present disclosure.

(5) FIG. 3A illustrates a schematic of a biosensor in communication with a controller in accordance with one embodiment of the present disclosure.

(6) FIG. 3B illustrates a schematic of a sensor unit comprising a biosensor and a controller in accordance with one embodiment of the present disclosure.

(7) FIG. 3C illustrates a schematic of a sensor unit comprising a plurality of biosensors and a controller in accordance with one embodiment of the present disclosure.

(8) FIG. 3D illustrates a schematic of a sensor unit comprising a biosensor, a controller, and a wireless communications module in accordance with one embodiment of the present disclosure.

(9) FIG. 3E illustrates a schematic of a sensor unit comprising a biosensor, a controller, a power source, an analog to digital converter, and a wireless communications module in accordance with one embodiment of the present disclosure.

(10) FIG. 4 illustrates a plurality of sensor units in wireless communication with a wireless gateway in accordance with one embodiment of the present disclosure.

(11) FIG. 5 provides a graph setting forth the results of an exposure test to about 7.5 ppm/min or ethylene. An ethylene biosensor was exposed to about 7.5 ppm/min of ethylene gas at standard atmospheric conditions within a confined about 5 L container. The voltage output correlated in a statistically significant manner to the overall ethylene concentration within the container.

(12) FIG. 6 provides a graph setting forth the results of an exposure test for about 10 to about 110 ppm of ethylene under standard atmospheric conditions. A biosensor was exposed from about 10 to about 110 ppm of ethylene. A reading was taken about at every 10 ppm.

(13) FIG. 7 provides a graph setting forth the results of ethylene testing using a biosensor of the present disclosure, where the ethylene concentration spike corresponds to quality control data, which indicated a change in fruit maturity.

(14) FIG. 8 illustrates a two-electrode system in accordance with one embodiment of the present disclosure.

(15) FIG. 9 illustrates a three-electrode system in accordance with the present disclosure.

DETAILED DESCRIPTION

(16) It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

(17) As used herein, the singular terms “a,” “an,” and “the” include plural referents unless context clearly indicates otherwise. Similarly, the word “or” is intended to include “and” unless the context clearly indicates otherwise. The term “includes” is defined inclusively, such that “includes A or B” means including A, B, or A and B.

(18) As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of” “only one of” or “exactly one of” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

(19) The terms “comprising,” “including,” “having,” and the like are used interchangeably and have the same meaning. Similarly, “comprises,” “includes,” “has,” and the like are used interchangeably and have the same meaning. Specifically, each of the terms is defined consistent with the common United States patent law definition of “comprising” and is therefore interpreted to be an open term meaning “at least the following,” and is also interpreted not to exclude additional features, limitations, aspects, etc. Thus, for example, “a device having components a, b, and c” means that the device includes at least components a, b and c. Similarly, the phrase: “a method involving steps a, b, and c” means that the method includes at least steps a, b, and c. Moreover, while the steps and processes may be outlined herein in a particular order, the skilled artisan will recognize that the ordering steps and processes may vary.

(20) As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

(21) The present disclosure is directed to a biosensor comprising a reference electrode and a counter electrode, wherein the reference electrode includes a layer comprising ethylene receptor molecules.

(22) FIG. 1 depicts a top-down view of a biosensor 10 in accordance with one embodiment of the present disclosure. In some embodiments, the biosensor 10 includes a reference electrode 2 and a counter electrode 3. In some embodiments, the reference electrode 2 and the counter electrode 3 are provided on substrate 1. In some embodiments, substrate 1 is a non-conductive substrate, such as a fiberglass epoxy resin or a phenolic resin. In some embodiments, the substrate is selected from carbon, fiberglass epoxy resin, phenolic resin, insulated metal substrate, polyimide film and fluoropolymer/polyimide film composites. In some embodiments, the biosensor 10 further comprises one or more leads, so as to allow the biosensor to communicate with other components and/or devices. In some embodiments, the leads are comprised of conductive tracks within the substrate, connecting to the reference electrode surface and the counter electrode. In some embodiments, the leads are comprised of the same metal in which the electrode is comprised. In some embodiments, the biosensor depicted in FIG. 1 includes one or more additional traces or leads.

(23) FIG. 8 sets forth a top down schematic of a two-electrode system in accordance with one embodiment of the present disclosure. In some embodiments, a reference electrode 101 of having metal composition which differs from the counter electrode 103 is separated by a gap 102. In some embodiments, an electrolytic mediator layer is posited proximal (e.g. atop) the two electrodes. Without wishing to be bound by any particular theory, it is believed that the electrolytic mediator layer promotes electron transfer between the reference electrode 101 and the counter electrode 103. In some embodiments, and upon a reaction between the ethylene receptor and ethylene (such as described herein), an oxidation reduction reaction catalyzes the movement of electrons from one electron to the other, which can be measured via current or voltage changes.

(24) FIG. 9 sets forth a top down schematic of a three-electrode system in accordance with another embodiment of the present disclosure. In some embodiments, the three-electrode system consists of three electrodes: a working electrode 105, a reference electrode 104, and a counter electrode 106. In some embodiments, the working electrode 105 includes an ethylene receptor protein (including any of those described herein). In some embodiments, it is believed that the ethylene receptor protein undergoes a reduction and oxidation reaction upon contact with one or more ethylene molecules, such as those ethylene molecules present in an environment (e.g. an environment surrounding the biosensor). In some embodiments, this is believed to generate an electrical potential between the working electrode 105 and the counter electrode 106. In some embodiments, an electrolytic mediator layer is positioned proximal (e.g. atop) the two electrodes and is believed to promote electron transfer between the working and counter electrodes 105 and 106, respectively. In some embodiments, the measured current is believed to pass through the working electrode and the third electrode, the counter electrode. In some embodiments, an electrolytic solution in the form of the mediator layer is in contact (e.g. placed between) at least two of the electrodes, e.g. all three of the electrodes, to provide ions to the electrodes during the oxidation and reduction reaction between ethylene and the ethylene receptor protein.

(25) In some embodiments, a three-electrode system permits stability advantages over the two-electrode system. With three electrodes, one can supply an external potential to the system, eliminating a variable. Theoretically, in a two-electrode system, ions are supplied due to galvanic corrosion of the two electrodes. In some embodiments, the potential generated between the two electrodes permits for the reaction of ethylene with ethylene receptor. However, it is difficult to control this ion supply, and thus the design of the two-electrode system presents greater stability issues than that of the three-electrode system. In some embodiments, the measurable output of a two-electrode system tends to be either voltage or resistance. Due to the variable nature of electron supply to the system, factors such as the external environment are more likely to affect the outputs of the system.

(26) In a three-electrode system, potential is supplied by one of the three electrodes, typically the reference electrode. Thus, there is a measurable quantity of ions supplied to the electrode system, and thus a stable baseline reading, typically of resistance. As such, any resistance change in the system is likely due to the binding event between ethylene and the ethylene receptor, generating a cleaner and more decipherable signal.”

(27) In some embodiments, and with reference to FIG. 2A, the reference electrode 2 comprises a receptor layer 5, a mediator layer 6, and a base electrode 7. The base electrode 7 may be comprised of any material known to those of ordinary skill in the art. For example, the base electrode 7 may be comprised of copper, gold, aluminum, or silver. In some embodiments, the base the electrode 7 may be comprised of indium tin oxide, gold, or silver electrodes. In some embodiments, the electrode 7 comprises a conductive metallic coating. In some embodiments, the metallic coating comprises copper and/or silver.

(28) FIG. 2B illustrates an alternative biosensor 10 having a reference electrode 2 including a receptor layer 5, a mediator layer 6, and an electrode 7. The biosensor depicted in FIG. 2B further includes a counter electrode 3 in communication with the receptor layer 5. In some embodiments, the counter electrode 3 is comprised of a material selected from gold, silver, copper, or any combination thereof. In some embodiments, the counter electrode 3 of FIG. 2B is comprised of a porous material, such as metal triazolates consisting of 1H-1,2,3-triazole and divalent metal ions (Mg, Mn, Fe, Co, Cu, and Zn). In other embodiments, the counter electrode of FIG. 2B includes one or more pores or punctures to facilitate the permeation of the ethylene gas through the counter electrode layer 3 and to the receptor layer 5. In some embodiments, the pores or punctures may have a radius ranging from between about 2 angstroms to about 2 mm.

(29) In some embodiments, the mediator layer 6 comprises a conductive and biocompatible material that serves to mediate electron transfer between the receptor layer and the metallic electrode. It is also believed that the mediator layer 6 serves to stabilize the components of the receptor layer, described herein. It is further believed that the mediator layer 6 facilitates crosslinking interactions with ethylene receptor proteins such that the ethylene receptor proteins become immobilized on the surface of the mediator layer 6. It is believed that electron movement resulting from reversible chemical interactions between ethylene and ethylene receptor molecules is encouraged due to the conductivity, and subsequent voltage output (between about 0 to about 7V), of the mediator layer.

(30) In some embodiments, the mediator layer 6 comprises at least one component selected from potassium ferricyanide, ferric chloride, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium chloride, naphthol green, or polypyrrole. In some embodiments, the mediator layer 6 comprises (i) a first component selected from potassium ferricyanide, ferric chloride, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium

(31) TABLE-US-00001 Name of layer Composition Prussian Blue about 0.05M potassium ferricyanide 3Fe(CN).sub.6 and about 0.05M ferric chloride both in about 5 mmol L.sup.−1 HCl Methyl Viologen about 10 μL glycerol, about 5 microliter nafion, about 20 microliter enzyme solution, about 10% w/v methyl viologen in about 20 mM 7.4 PBS, reticulated in saturated glutaraldehyde vapor Ferrocene about 1% (w/w) Nafion solution (in EtOH), about 0.05M ferrocene solution in DI water, about 5 mg/mL ethylene receptor solution, about 4 microliters/mL glutaraldehyde solution (25%, aqueous) Cysteamine between about 1.2 to about 2.9M cysteamine, about 2 mg/ml of enzyme 3-mercaptopropionic acid about 1.2M 3-mercaptopropionic acid, about 30 mM EDC and about 15 mM NHS, about 5 mg/mL ethylene receptor solution 4-mercaptobenzoic acid about 1.2M 4-mercaptobenzoic acid solution, about 30 mM EDC and about 15 mM NHS, about 5 mg/mL ethylene receptor solution 11-mercaptoundecanoic acid about 1.2M 11-mercaptoundecanoic acid, about 30 mM EDC and about 15 mM NHS, 5 mg/mL ethylene receptor solution Ruthenium purple about 1 mM of RuCl3solution including about 1 mM KCl Naphthol Green B about 4 mmol/L naphthol green, about 3 mg/mL ethylene receptor solution (Os-(bpy)PVI) about 8-μL of a 6-mg/ml (Os(bpy)2PVI), about 1.9 μL of a about 15-mg/mL aqueous solution of PEGDGE and about 4.8 μL of 10-mg/ml ethylene solution Polypyrrole PVDF granules in DMF (about 2% W/V) added to FeCl.sub.3 to which about 2% polypyrrole is added

(32) chloride, naphthol green, or polypyrrole; and (ii) a second component.

(33) In some embodiments, the mediator layer 6 comprises the components set forth in Table 1 below.

(34) Table 1 provides a listing of mediator layers which may be utilized and the components of each of those mediator layers.

(35) In some embodiments, the receptor layer 5 comprises an ethylene receptor protein. The term “ethylene receptor” or “ethylene receptor protein,” refers to ethylene receptors from any of the ethylene receptor families present in a plant. By way of example, in Arabidopsis, ethylene receptor proteins include ETR1, ERS1, ETR2, ERS2, and EIN4. Zea mays ethylene receptor proteins include ZmERS1 and ZmETR2 (including the ZmETR2 variants ZmETR9 and ZmETR40). In some embodiments, the ethylene receptor proteins are derived from the genes of Lactuca Sativa, Bryophyta, Petunia, and Solanum lycopersicum may also be used. Methods of isolating ethylene receptors are described herein, and also described in U.S. Pat. Nos. 7,951,993 and 7,105,654, the disclosures of which are hereby incorporated by reference herein in their entireties.

(36) Ethylene receptors of the present disclosure may be isolated from any species of plant and include species homologs of the exemplary ethylene receptors. In that regard, in some embodiments, the ethylene receptor protein is naturally occurring. Examples of naturally occurring ethylene receptors include ethylene receptor 1 (ETR1) (such as derived from ARABIDOPSIS THALIANA), ethylene receptor 2 (ETR 2) (such as derived from ARABIDOPSIS THALIANA), ethylene receptor 3 (ETR3) (such as derived from ORYZA SATIVA INDICA), or ethylene receptor 4 (ETR4) (such as derived from ORYZA SATIVA JAPONICA).

(37) In some embodiments, the ethylene receptor protein comprises a nucleotide sequence which is at least 90% identical to a wild-type polynucleotide sequence of an ethylene receptor gene. In some embodiments, the ethylene receptor protein comprises a nucleotide sequence which is at least 95% identical to a wild-type polynucleotide sequence of an ethylene receptor gene. In some embodiments, the ethylene receptor protein comprises a nucleotide sequence which is at least 97% identical to a wild-type polynucleotide sequence of an ethylene receptor gene. In some embodiments, the ethylene receptor protein comprises a nucleotide sequence which is at least 98% identical to a wild-type polynucleotide sequence of an ethylene receptor gene. In some embodiments, the ethylene receptor protein comprises a nucleotide sequence which is at least 99% identical to a wild-type polynucleotide sequence of an ethylene receptor gene.

(38) In some embodiments, the ethylene receptor has at least 80% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 85% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 90% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 95% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 96% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 97% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 98% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor has at least 99% identity to the amino acid sequence of SEQ ID NO: 1. In some embodiments, the ethylene receptor comprises the amino acid sequence of SEQ ID NO: 1.

(39) In some embodiments, the ethylene receptor has at least 80% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 85% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 90% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 95% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 96% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 97% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 98% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor has at least 99% identity to the amino acid sequence of SEQ ID NO: 2. In some embodiments, the ethylene receptor comprises the amino acid sequence of SEQ ID NO: 2.

(40) In some embodiments, the ethylene receptor has at least 80% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 85% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 90% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 95% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 96% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 97% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 98% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor has at least 99% identity to the amino acid sequence of SEQ ID NO: 3. In some embodiments, the ethylene receptor comprises the amino acid sequence of SEQ ID NO: 3.

(41) In some embodiments, the ethylene receptor has at least 80% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 85% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 90% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 95% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 96% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 97% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 98% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor has at least 99% identity to the amino acid sequence of SEQ ID NO: 4. In some embodiments, the ethylene receptor comprises the amino acid sequence of SEQ ID NO: 4.

(42) In other embodiments, the ethylene receptors also include proteins with naturally-occurring and induced mutations, including insertion, deletion, and point mutations. In yet other embodiments, the ethylene receptor protein is non-naturally occurring.

(43) In some embodiments, between about 10 to about 1000 nanograms of ethylene receptor are protein are included within the receptor layer. In some embodiments, between about 20 to about 600 nanograms of ethylene receptor protein is included within the receptor layer. In some embodiments, between about 50 to about 300 nanograms of ethylene receptor protein is included within the receptor layer. In some embodiments, about 0.015 milligrams of ethylene receptor protein applied for every cubic centimeter of the components of the mediator layer applied. In some embodiments, about 0.04 milligrams of ethylene receptor protein are applied for every cubic centimeter of the components of the mediator layer applied. In some embodiments, about 0.002 milligrams of ethylene receptor protein are applied for every cubic centimeter of the components of the mediator layer applied.

(44) In some embodiments, the overall thickness of the reference electrode ranges from between about 0.1 mm to about 1.5 mm. In some embodiments, each of the individual layers of the reference electrode do not exceed about 1 mm in thickness.

(45) The ethylene receptors described above may be isolated and collected according to any process known to those of ordinary skill in the art. For example, ethylene receptor production may include the steps of (1) expressing ethylene-binding proteins in a vector host; (2) amplifying vector hosts to desired volumes; and (3) extracting/isolating desired proteins from the vector hosts. In some embodiments, gene sequences for proteins capable of binding to ethylene are expressed within a plasmid capable of being expressed by the vector host. Vector hosts are typically prokaryotic cells but may also include eukaryotic cells as well. The plasmid within which the gene sequence is inserted must be able to be translated by the vector host. Upon successful insertion of the plasmid into the vector host, the host is amplified. In bacteria, amplification typically involves culturing bacterial hosts within a broth solution for about 8 to about 12 hours. Following incubation of bacterial host with broth, the resulting bacteria is centrifuged, and protein isolation methods are performed. The means of protein extraction can be chemical, through the means of a detergent, or mechanical, such as sonication or heat treatments. An alternative means of protein extraction is by attaching a specific tag to the plasmid, such as a histidine tag, and using a column to purify his-tagged proteins. Other methods of isolating and collecting ethylene receptors are described in U.S. Patent Publication Nos. 2002/0012982A1 and US20020127587A1; U.S. Pat. Nos. 4,431,739, 4,366,246, and 3,585,179; and also, in EP0001929B1 and EP0001929A2, the disclosures of which are hereby incorporated by reference herein in their entireties.

(46) Without wishing to be bound by any particular theory, it is believed that when an ethylene gas molecule 8 binds to the ethylene receptor molecules within the receptor layer 5, electron transfer occurs (see FIGS. 2A and 2B, where an ethylene molecule 8 is bound to an ethylene receptor in the receptor layer 5). In the case of the presently disclosed biosensors, the electron transfer may be passed from the receptor layer 5 to the mediator layer 6 and ultimately to the electrode 7 (see FIGS. 2A and 2B). It is further believed that multiple binding events generate electron movement that can be measured as a voltage change. The resulting voltage change can be linearly correlated to the concentration of atmospheric ethylene. It is believed that the correlation can be made by exposing the ethylene sensor to a standard of known ethylene gas concentrations and measuring the resulting voltage output. For example, over the course of a period of time, one can expose the ethylene sensor to increasing parts per million of ethylene and measure the change in voltage. These data points can then be used to estimate a linear equation correlating voltage output to ethylene binding to the sensor and resulting air concentrations of ethylene.

(47) The biosensor 10 may be fabricated according to any method known to those of ordinary skill in the art. In some embodiments, a solution comprising the desired components of the mediator layer are drop coated onto an electrode 7 or a coated electrode 7. The components of any mediator layer 6 and the concentrations of those components relative to each other are described above in Table 1. Following the deposition of the mediator layer 6, the receptor layer 5 may be drop coated onto the mediator layer. In some embodiments, the ethylene receptor protein is included within a buffer solution and the solution is applied to a dried mediator layer 5 to provide the receptor layer 6 (upon its drying). The receptor solution typically consists of a solution with a pH range of about 7 to about 9 for the lysis of proteins. A typical lysis buffer solution contains about 50 to about 100 mM Tris-HCl, about 100 to about 300 mM NaCl, about 1 mM Dithiothreitol (DTT) or about 1% NP-40. Additionally, protease inhibitors or protease inhibitor cocktails may be added to the buffer solution following protein lysis. Alternative buffer solutions are shown in Table 2.

(48) Table 2 lists buffers and their corresponding pKa values. Any of the ethylene receptor proteins described herein may be provided in solution with any of the buffers of Table 2.

(49) TABLE-US-00002 pKa at Buffer 20° C. MES 6.15 Bis-tris methane 6.60 ADA 6.62 N-(2-Acetamido)-2-aminoethanesulfonic acid (ACES) 6.76 Bis-tris propane 6.80 piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES) 6.82 3-Morpholino-2-hydroxypropanesulfonic acid (MOPSO) 6.95 Cholamine chloride 7.10 3-(N-morpholino)propanesulfonic acid (MOPS) 7.15 bis(2-hydroxyethyl)amine (BES) 7.17 2-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2- 7.5 yl]amino]ethanesulfonic acid (TES) (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) 7.55 (HEPES) [3-Bis(2-hydroxyethyl) amino-2-hydroxypropane-1- 7.6 sulfonic acid] (DIPSO) 4-(N-Morpholino)butanesulfonic acid (MOBS) 7.6 Acetamidoglycine 7.7 3-[[1,3-dihydroxy-2-(hydroxymethyl)propan-2-yl]amino]- 7.6 2-hydroxypropane-1-sulfonic acid (TAPSO) tris(hydroxymethyl)aminomethane - acetate- 7.8 Ethylenediaminetetraacetic acid (TEA) [Piperazine-1,4-bis(2-hydroxy-3-propanesulfonic 7.85 acid),dihydrate] (POPSO) ((2-Hydroxyethyl)-piperazine-N-2-hydroxypropanesulfonic 7.9 acid) (HEPPSO) EPS 8.0 3-[4-(2-Hydroxyethyl)piperazin-1-yl]propane-1-sulfonic 8.1 acid (HEPPS) N-(2-Hydroxy-1,1-bis(hydroxymethyl)ethyl)glycine 8.15 (Tricine) tris(hydroxymethyl)aminomethane 8.2 Glycinamide 8.2 Glycylglycine 8.2 N-(2-Hydroxyethyl)piperazine-N'-(4-butanesulfonic acid) 8.3 (HEPBS) 2-(Bis(2-hydroxyethyl)amino)acetic acid (Bicine) 8.35 3-{[1,3-dihydroxy-2-(hydroxymethyl)propan-2- 8.55 yl]amino}propane-1-sulfonic acid (TAPS) 2-Amino-2-Methyl-1-Propanol (AMP) 8.8 2-(Cyclohexylamino)ethanesulfonic acid (CHES) 9.3 ((1,1-Dimethyl-2-hydroxyethyl)amino)-2- 9.0 hydroxypropanesulfonic acid sodium salt (AMPSO) N-cyclohexyl-2-hydroxyl-3-aminopropanesulfonic acid 9.6 (CAPSO) 3-(Cyclohexylamino)-1-propanesulfonic acid (CAPS) 10.4

(50) In another aspect of the present disclosure is a sensor unit 20 incorporating one or more of the biosensors 10 of the present disclosure. As depicted in FIGS. 3A and 3B, the sensor unit 20 may be coupled to a controller 11 such that current changes due to the binding of ethylene to the ethylene receptor molecules may be measured and/or recorded. In some embodiments, the sensor unit 20 comprises a biosensor 10 and a controller 11, where the biosensor 10 and controller 11 are provided in separate housings (FIG. 3A). Alternatively, the sensor unit 20 comprises a biosensor 10 and a controller 11, where the biosensor 10 and controller 11 are coupled together, such as within the same housing or where both are provided on a chip. FIG. 3C illustrates a sensor unit 20 comprising at least two biosensors 10, each independently in communication with a controller 11. While FIG. 3C illustrates a sensor unit 20 comprising only two biosensors 10, the skilled artisan will appreciate that any number of biosensors 10 may be coupled to a single controller 11, e.g. 3, 4, 5, 10, or more biosensors.

(51) In some embodiments, the controller includes a wireless communication module. In some embodiments, the wireless communications module is included within the controller 11 (i.e. within the same chip or module). In other embodiments, and with reference to FIG. 3D, the wireless communications module 12 is separate from controller 11. In some embodiments, and with reference to FIG. 3E, sensor unit 20 may comprise one or more biosensors 10; a power supply 13; a wireless communication module 12; and an analog to digital converter 14. In some embodiments, each sensor unit 20 may further comprise a memory module, e.g. volatile (e.g. RAM, etc.) and non-volatile (e.g. ROM, flash-memory, etc.) memory, additional processors or programmable circuits, other communication means (e.g. wired network communication), timers, oscillators, motion detectors, GPS modules, or any other helper device or circuit.

(52) In some embodiments, multiple sensor units 20 may be in wireless communication with each other or in wireless communication with a gateway 30, a server 31, storage device, etc. (see FIG. 4). In some embodiments, each sensor unit 20 may communicate via infrared pulses, radio waves, ultrasonic waves, or another wireless communication medium. In some embodiments, wireless communications are through a standard protocol, for example a Zigbee mesh network, LoRaWAN, 802.11 WiFi, or Bluetooth. Proprietary solutions could also be used. Wireless communication protocols will typically be accomplished using integrated circuits or modules specifically designed for the purpose. Modules appropriate for the purpose include those manufactured by, for example, Digi International, Synapse Wireless, Motorola, or Panasonic.

(53) In some embodiments, the sensor units 20 have means for communicating with each other, with the wireless gateway, and/or with other network units, thus establishing a sensor network of any suitable kind. A network of the sensor units (a “sensor network”) may be more or less organized, with none or any level of central control. In some embodiments, the wireless gateway may act as a common network controller for organizing the wireless sensors, e.g. by assigning IP-addresses in an IP network configuration. In some embodiments, the wireless gateway is a network unit that avails access in some sense between the individual sensor units of the sensor network and one or more external units. The wireless gateway may, for example, comprise a conventional wireless network gateway hardware for establishing access and routing between different networks, e.g. the wireless sensors with WiFi capabilities and the Internet or any other network, or e.g. a GSM or other cellular network communication unit. The wireless gateway may thus comprise one or more of the functionalities and tasks of conventional gateways, access points, routers, bridges, network address assigning or resolving, security controllers, web servers, etc. In some embodiments, the wireless gateway also carries out the task of collecting and possibly refining data and information from the individual sensor units of the sensor network.

(54) In addition, the wireless gateway 30 may comprise a sensor unit 20 or it may be a sensor-free unit entirely dedicated to collecting data from all the sensor units 20. The wireless gateway 30 may further comprise positioning means for obtaining an initial position for itself, e.g. by means of a GPS unit which is feasible if located outside the biomass and heavy buildings or containers. The gateway 30 may also be provided with its position manually by the user, or it may simply be defining the center of the world as far as the sensor units 20 are concerned, i.e. the origin or other reference position in their positioning grid.

(55) In some embodiments, the biosensor 10 is calibrated by exposing it to fixed concentrations of ethylene, and the voltage is measured. A linear correlation between voltage and ethylene concentration is established, and this standard can be used to measure ethylene concentrations outside of the tested range.

EXAMPLES

(56) Receptor Isolation

(57) Ethylene receptor genes expressed via plasmid, such as ETR1, ETR2, or ETR3, were transformed into bacteria. Following transformation, bacteria were streaked onto an agar plate, and after 12-24 hrs of incubation colonies form upon the surface. If using an antibacterial resistance plasmid, the agar should also contain the selected antibiotic. Colonies were picked and sequenced to ensure proper insertion of plasmidic DNA. Following the selection of properly expressing colonies, bacteria were amplified in LB broth for the desired yield. Typically, bacteria are grown in between 2 mL-1 L of broth for 12-18 hrs at 37 degrees Celsius.

(58) Following bacterial growth, the bacteria were centrifuged, and the LB broth was removed. The bacterial pellet was treated with a protein extraction agent, and protein extraction was performed according to protocols specific to the reagent used. Specific protein isolation could be performed via centrifugation, if the protein is of known concentration, via antibody pulldown protocols, or by amending the plasmidic sequence to include a specific binding site, such as a poly-histidine tail, and using an affinity column to isolate the protein.

(59) Biosensor Testing 1

(60) An ethylene biosensor including the components described herein (about 200 uL of about 10% pyrrole mediator layer with about 0.015 mg/mm of Arabidopsis ETR1 upon an about 2 square inch copper electrode) was placed into a 5 L airtight vacuum chamber at standard atmospheric conditions. A biosensor consisting of an aluminum electrode, pyrrole mediator, and 100 ng of protein was exposed to ethylene at a concentration of about 0.125 ppm/sec for about 375 seconds. The voltage output of the sensor was measured continuously during ethylene exposure (see FIG. 5). Voltage outputs correlated linearly with linear exposure of ethylene to the biosensor, establishing a standard relationship between voltage and ethylene concentration. This correlation was statistically significant, with an R-squared value of about 0.97. The resulting equation generated by correlating ethylene exposure to voltage output, can be used to predict ethylene concentrations outside of the standard's bounds. This standard was replicated for a greater range of ethylene concentrations in FIG. 6, which analyzed the performance of a biosensor with a copper electrode, about 100 uL of pyrrole mediator, and about 100 uL of protein. This figure supported the linear relationship between voltage and ethylene concentration for a greater range of ethylene concentrations.

(61) Biosensor Testing 2

(62) The sensor (about 200 uL of an about 5% pyrrole mediator with about 0.015 mg/mm of Arabidopsis ETR1 upon a two square inch aluminum electrode) was tested within controlled atmosphere storage of apples. Depicts an experiment conducted for a period of 82 days within a controlled atmosphere storage room kept at 1 degree Celsius, about 2% O2, and about 0.6% CO.sub.2, with 2,000 bins of honey crisp apples. On day 70, the relative ethylene concentration within the controlled atmosphere storage room spiked, indicating the beginning of senescence for the fruit within the storage room (see FIG. 8). Using this data, a prediction was made for the room based on the senescence curve of honey crisp apples that the storage room had 1-2 months prior to experiencing significant maturity related losses due to fruit senescence. This data correlated with quality control data of fruit samples pulled from the room following its opening. This result indicates the predictive ability of an ethylene sensor in determining fruit senescence, which may be used to mitigate losses within the food supply chain.

(63) Additional Embodiment 1: A biosensor comprising: (a) a reference electrode comprising (i) a mediator layer deposited on a base electrode; and (ii) a receptor layer deposited on the mediator layer, wherein the receptor layer comprises an ethylene receptor; (b) a counter electrode in communication with the reference electrode; and (c) a working electrode. Additional Embodiment 2: The biosensor of additional embodiment 1, wherein the base electrode is comprised of a material selected from the group consisting of copper and silver.

(64) Additional Embodiment 3: The biosensor of additional embodiment 1, wherein the base electrode comprises a coating of a material selected from the group consisting of copper and silver.

(65) Additional Embodiment 4: The biosensor of additional embodiment 1, wherein the ethylene receptor comprises a nucleotide sequence having at least 90% sequence identity to a wild-type polynucleotide sequence of an ethylene receptor gene.

(66) Additional Embodiment 5: The biosensor of additional embodiment 1, wherein the ethylene receptor is derived from Zea mays or Arabidopsis.

(67) Additional Embodiment 6: The biosensor of additional embodiment 1, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 1.

(68) Additional Embodiment 7: The biosensor of additional embodiment 1, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 2.

(69) Additional Embodiment 8: The biosensor of additional embodiment 1, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 3.

(70) Additional Embodiment 9: The biosensor of additional embodiment 1, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 4.

(71) Additional Embodiment 10: The biosensor of additional embodiment 1, wherein the receptor layer comprises between about 10 to about 1000 nanograms of ethylene receptor.

(72) Additional Embodiment 11: The biosensor of additional embodiment 1, wherein the mediator layer comprises at least one of potassium ferricyanide, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium chloride, naphthol green, or polypyrrole.

(73) Additional Embodiment 12: A stack comprising: (a) a mediator layer, and (b) a receptor layer in contact with the mediator layer, wherein the receptor layer comprises one or more ethylene receptor proteins.

(74) Additional Embodiment 13: The stack of additional embodiment 12, wherein the one or more ethylene receptor proteins are selected from the group consisting of ETR1, ETR2, ETR3, and ETR4.

(75) Additional Embodiment 14: The stack of additional embodiment 12, wherein the one or more ethylene receptor proteins comprises an amino acid sequence having at least 90% identity to any of SEQ ID NOS: 1-4.

(76) Additional Embodiment 15: The stack of additional embodiment 12, wherein the receptor layer comprises between about 0.038 mg/mm to about 0.38 mg/mm nanograms of ethylene receptor proteins.

(77) Additional Embodiment 16: The stack of additional embodiment 12, wherein the mediator layer comprises at least one of potassium ferricyanide, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium chloride, naphthol green, or polypyrrole.

(78) Additional Embodiment 17: A reference electrode comprising the stack of any one of additional embodiments 12 to 16 deposited on a base electrode.

(79) Additional Embodiment 18: The reference electrode of additional embodiment 17, wherein the base electrode comprises a coating including copper or silver.

(80) Additional Embodiment 19: A biosensor comprising the reference electrode of any one of additional embodiments 17-18; and a counter electrode in communication with the reference electrode.

(81) Additional Embodiment 20: A sensor unit comprising the biosensor of any one of additional embodiments 1 to 11 and 19; and a controller in communication with the biosensor.

(82) Additional Embodiment 21: The sensor unit of additional embodiment 20, wherein the controller comprises a communication module.

(83) Additional Embodiment 22: The sensor unit of additional embodiment 21, wherein the communication module is a wireless communication module.

(84) Additional Embodiment 23: A system comprising a plurality of the sensor units of additional embodiment 22, wherein the plurality of sensor units are each independently in wireless communication with a receiver module, gateway, or storage module.

(85) Additional Embodiment 24: A container comprising at least one of the sensor units of any one of additional embodiments 20 to 22.

(86) Additional Embodiment 25: A biosensor comprising: (a) a reference electrode comprising (i) a mediator layer deposited on a base electrode; and (ii) a receptor layer deposited on the mediator layer, wherein the receptor layer comprises an ethylene receptor; and (b) a counter electrode in communication with the reference electrode.

(87) Additional Embodiment 26: The biosensor of additional embodiment 25, wherein the base electrode is comprised of a material selected from the group consisting of copper and silver.

(88) Additional Embodiment 27: The biosensor of additional embodiment 25, wherein the base electrode comprises a coating of a material selected from the group consisting of copper and silver.

(89) Additional Embodiment 28: The biosensor of additional embodiment 25, wherein the ethylene receptor comprises a nucleotide sequence having at least 90% sequence identity to a wild-type polynucleotide sequence of an ethylene receptor gene.

(90) Additional Embodiment 29: The biosensor of additional embodiment 25, wherein the ethylene receptor is derived from Zea mays or Arabidopsis.

(91) Additional Embodiment 30: The biosensor of additional embodiment 25, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 1.

(92) Additional Embodiment 31: The biosensor of additional embodiment 25, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 2.

(93) Additional Embodiment 32: The biosensor of additional embodiment 25, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 3.

(94) Additional Embodiment 33: The biosensor of additional embodiment 25, wherein the ethylene receptor comprises an amino acid sequence having at least 90% identity to that of SEQ ID NO: 4.

(95) Additional Embodiment 34: The biosensor of additional embodiment 25, wherein the receptor layer comprises between about 10 to about 1000 nanograms of ethylene receptor.

(96) Additional Embodiment 35: The biosensor of additional embodiment 25, wherein the mediator layer comprises at least one of potassium ferricyanide, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium chloride, naphthol green, or polypyrrole.

(97) Additional Embodiment 36: A stack comprising: (a) a mediator layer, and (b) a receptor layer in contact with the mediator layer, wherein the receptor layer comprises an ethylene receptor protein.

(98) Additional Embodiment 37: The stack of additional embodiment 36, wherein the ethylene receptor protein is selected from the group consisting of ETR1, ETR2, ETR3, and ETR4.

(99) Additional Embodiment 38: The stack of additional embodiment 36, wherein the ethylene receptor protein comprises an amino acid sequence having at least 90% identity to any of SEQ ID NOS: 1-4.

(100) Additional Embodiment 39: The stack of additional embodiment 36, wherein the receptor layer comprises between about 0.038 mg/mm to about 0.38 mg/mm nanograms of ethylene receptor proteins.

(101) Additional Embodiment 40: The stack of additional embodiment 36, wherein the mediator layer comprises at least one of potassium ferricyanide, methyl viologen, ferrocene, cysteamine, mercaptopropionic acid, mercaptobenzoic acid, mercaptoundecanoic acid, ruthenium chloride, naphthol green, or polypyrrole.

(102) Additional Embodiment 41: A reference electrode comprising the stack of any one of additional embodiments 12 to 16 deposited on a base electrode.

(103) Additional Embodiment 42: The reference electrode of additional embodiment 41, wherein the base electrode comprises a coating including copper or silver.

(104) Additional Embodiment 43: A biosensor comprising the reference electrode of any one of additional embodiments 17-18; and a counter electrode in communication with the reference electrode.

(105) Additional Embodiment 44: A sensor unit comprising the biosensor of any one of additional embodiments 1 to 11 and 19; and a controller in communication with the biosensor.

(106) Additional Embodiment 45: The sensor unit of additional embodiment 44, wherein the controller comprises a communication module.

(107) Additional Embodiment 46: The sensor unit of additional embodiment 45, wherein the communication module is a wireless communication module.

(108) Additional Embodiment 47: A system comprising a plurality of the sensor units of additional embodiment 22, wherein the plurality of sensor units are each independently in wireless communication with a receiver module, gateway, or storage module.

(109) Additional Embodiment 48: A container comprising at least one of the sensor units of any one of additional embodiments 44 to 46.