FUNCTIONALIZED DIACETYLENE MONOMERS, THEIR POLYMERIZATION AND USES THEREOF

Abstract

An aminochalcone-diacetylene compound of Formula 1A:

##STR00001##

wherein R.sup.1 and R.sup.2 are independently selected from H and C.sub.1-C.sub.3 alkyl, A denotes a linkage connecting the chalcone and diacetylene units, m and n are independently integers in the range of 2 to 18, and the corresponding protonated form/ammonium salt of Formula 1B:

##STR00002##

wherein X is a counter anion. The disclosure further discloses the corresponding chromatic polydiacetylenes and polydiacetylenes-based sensors for detecting ammonia.

Claims

1. An aminochalcone-diacetylene compound of Formula 1A: ##STR00018## wherein R.sup.1 and R.sup.2 are independently selected from H and C.sub.1-C.sub.3 alkyl, A denotes a linkage connecting the chalcone and diacetylene units, m and n are independently integers in the range of 2 to 18, and the corresponding protonated form/ammonium salt of Formula 1B: ##STR00019## wherein X is a counter anion.

2. A compound of Formula 1A or 1B according to claim 1, wherein the linkage A comprises an ester bond or an amide bond.

3. A compound of Formula 1A or 1B according to claim 2, wherein the linkage A is an ester bond.

4. A compound of Formula 1A or 1B according to claim 1, wherein the linkage A and the NR.sup.1R.sup.2 group are both at the para positions of the respective rings.

5. The compound of Formula 1B according to claim 1, wherein X is chloride.

6. A compound of Formula 1A or 1B according to claim 1, wherein the compound is N,N-dialkylated.

7. The compound of Formula 1A according to claim 1, which is ##STR00020##

8. A process for preparing a compound of Formula 1A comprising reacting a diacetylene compound of Formula 2 and aminochalcone of Formula 3: ##STR00021## wherein n, m, R.sup.1, R.sup.2 and A are as defined in claim 1, A and A are functional groups which participate in a linkage formation reaction, to create a linkage A.

9. The process according to claim 8, comprising reacting an alcohol of Formula 3, wherein A is OH, and an acyl chloride of Formula 2, wherein A is C(O)Cl, in an organic solvent in the presence of amine catalyst, to form the corresponding ester of Formula 1A, wherein A is OC(O).

10. A process comprising: assembling a chalcone-diacetylene of Formula 1A into a thin film; treating the thin film with gaseous acid, to form the compound of Formula 1B; and photopolymerizing the compound of Formula 1B to afford the corresponding polydiacetylene of Formula 5: ##STR00022## wherein R.sup.1 and R.sup.2 are independently selected from H and C.sub.1-C.sub.3 alkyl, A is an ester bond or an amide bond, m and n are integers in the range of 2 to 18 and X is a counter anion.

11. A chalcone-polydiacetylene of Formula 5: ##STR00023## wherein R.sup.1 and R.sup.2 are independently selected from H and C.sub.1-C.sub.3 alkyl, A is an ester bond or an amide bond, m and n are integers in the range of 2 to 18 and X is a counter anion.

12. The chalcone-polydiacetylene of Formula 5 according to claim 11, wherein R.sup.1 and R.sup.2 are both methyl, A is an ester bond OC(O), wherein the linkage A and the NR.sup.1R.sup.2 group are both at the para positions of the respective rings, n equals 6, m equals 8 and X is chloride.

13. A colorimetric and/or fluorescent sensor for detection of vapors of ammonia and related amine compounds, comprising the chalcone-polydiacetylene of Formula 5 as defined in claim 11.

14. A colorimetric and/or fluorescent sensor for detection of biogenic ammonia and related amines compounds, comprising the chalcone-polydiacetylene of Formula 5 as defined in claim 11.

15. A colorimetric and/or fluorescent sensor for monitoring food spoilage, comprising the chalcone-polydiacetylene of Formula 5 as defined in claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIGS. 1A-1C show the results of the treatment of CHA-DA films with different acids and subsequent polymerization.

[0042] FIGS. 2A-2C show spectroscopic characterization of chalcone-functionalized polydiacetylene. More specifically, FIG. 2A: UV-vis absorption spectra of the non-polymerized and polymerized diacetylene species. FIG. 2B: Raman spectra. The broken vertical lines indicate the (CC) and (CC) stretching frequencies, respectively, in HCl-treated chalcone-PDA. FIG. 2C: FTIR spectra showing NH vibration frequency domain. The broken vertical line indicates the NH stretching frequency of chalcone-diacetylene-HCl.

[0043] FIGS. 3A-3Cshow the thermochromic properties of the HCl-treated chalcone-PDA film that was deposited on filter paper. More specifically, FIG. 3A: photographs of HCl-treated chalcone-PDA film drop-casted on a filter paper at different temperatures. FIG. 3B: UV-vis absorbance spectra. FIG. 3C: Raman spectra of the HCl-treated chalcone-PDA film at different temperatures.

[0044] FIG. 4A shows the color (top row) and fluorescence (bottom row) transformations of the HCl-treated chalcone-PDA film upon brief exposure to ammonia gas at 20 C. and at 20 C. FIG. 4B depicts the deprotonation process caused by the ammonia vapors. FIG. 4C shows the fluorescence modulation induced upon exposure of the HCl-treated polymerized chalcone-PDA film to ammonia vapor, and the linear relationship between the fluorescence enhancement and ammonia concentration. FIG. 4D shows fluorescence enhancement following the action of different organic amines on the PDA film.

[0045] FIGS. 5A-5C show photos of a visual bacterial sensing test of the HCl-treated chalcone-PDA films, and fluorescence enhancement versus bacteria cell/ml curve.

[0046] FIGS. 6A-6B show photos of HCl-treated chalcone-PDA films, sensing ammonia generated by bacterial proliferation in fish samples.

DETAILED DESCRIPTION

Materials

[0047] 4-dimethylaminobenzaldehyde was purchased from Sigma Aldrich (Bangalore, India), and 4-hydroxyacetophenone was purchased from Sigma Aldrich (Shanghai, China). Sodium hydroxide and organic solvents including hexane, dichloromethane, chloroform, acetone, ethyl acetate and ethanol were purchased from Bio-Lab Ltd. (Jerusalem, Israel). All these chemicals were used without further purification. 10,12-tricosadiynoic acid (TRCDA) was purchased from Alfa Aesar (Lancashire, England) and purified prior to use by dissolving in chloroform and passing using a 0.8 m syringe filter followed by solvent removal by rotary evaporation.

Methods

[0048] Ultraviolet-visible (UV-vis) spectra: The samples for thin-film measurements were prepared by drop-casting 50 L of 15 mg/mL solution of the desired compound onto glass substrates. UV-vis spectra were recorded on an Evolution 220 UV-visible spectrometer (Thermo Scientific, Madison, WI). For solid-state UV-vis spectroscopy, the samples coated on thin film were analyzed in the wavelength range of 300-700 nm.

[0049] Fluorescence spectroscopy: The measurements were carried out using a Fluorolog spectrophotometer (HORIBA Scientific, Irvine, CA). For the analysis, thin-film samples were prepared by drop-casting 50 L of 15 mg/mL solution onto glass substrates; the paper probes were prepared by drop-casting 5 L of 15 mg/mL solution onto Whatman (grade 1) filter paper.

[0050] Fourier-transform infrared spectroscopy (FTIR): The measurements were performed on a Thermo Scientific Nicolet 6700 spectrometer in ATR mode. The sample was prepared by drop-casting 15 mg/mL solution of the desired compound onto glass substrates.

[0051] Raman scattering: The measurements were performed on a LabRam HR-high resolution analytical Raman (Horiba Jobin Yvon, France). The excitation source was a 753 nm laser, and 50long-focal-length objective lenses were employed. The sample was prepared by drop-casting 15 mg/mL of the desired compound solution onto glass substrates.

[0052] Scanning electron microscopy (SEM): The images were obtained on a JEOL scanning electron microscope (Tokyo, Japan, JSM-7400F). For SEM imaging, the corresponding samples were coated with gold and imaged at different magnifications.

[0053] Nuclear magnetic resonance (NMR): The spectra were recorded on a Bruker DPX 400 spectrometer using CDCl3 as a solvent and tetramethylsilane (TMS) as an internal standard. Chemical shifts are relative to TMS. MestreNova software was used for analyzing the NMR data.

Example 1

Synthesis of chalcone-substituted diacetylene monomer bearing protonatable amine group (CHA-DA)

Part A: Preparation of CHA

[0054] A round-bottomed flask was charged with ethanol (10 ml) and 10% sodium hydroxide (5 ml) followed by 4-(dimethylamino)benzaldehyde (745 mg, 5 mmol), and the mixture was stirred to complete dissolution. 1-(4-Hydroxyphenyl) ethan-1-one (816 mg, 6 mmol) was added, and the reaction mixture was stirred at RT for 24 hours. After the reaction, HCl solution was added to quench the reaction, and the aqueous layer was extracted with EA (50 mL3). The combined organic layers were washed with brine (50 mL), dried over Na.sub.2SO.sub.4 and concentrated. The solvent was removed under reduced pressure and the residue was chromatographed on silica gel (Petroleum Ether/Ethyl acetate) to afford 910 mg of desired product CHA (68% yield).

Part B: Preparation of CHA-DA

[0055] A round-bottomed flask was charged with 10,12-tricosadiynoic acid (TRCDA, 2.6 mmol, 900 mg) and dichloromethane (DCM, 20 mL) to obtain a solution. Oxalyl chloride (0.45 mL, 5.2 mmol) was added, and the mixture was stirred for 30 min at room temperature. N,N-dimethylformamide (DMF, catalytic amounts-2-3 drops) was added to the solution and the reaction mixture was stirred for 4.5 hours. The solvents and excess oxalyl chloride were removed by a rotary evaporator under a vacuum to give acyl chloride of 10,12-tricosadiynoic acid (TRCDA-Cl). The TRCDA-Cl residue was dissolved in DCM (10 mL) and the solution was directly used in the next step.

[0056] (E)-3-(4-(dimethylamino)phenyl)-1-(4-hydroxyphenyl) prop-2-en-1-one (CHA, 534 mg, 2 mmol) was dissolved in DCM (10 mL) in a separate flask, followed by the addition of triethyl amine (3 mmol, 0.417 mL). Then the acyl chloride solution (from the previous step) was added dropwise to the reaction mixture and once the addition is completed the resultant solution was stirred at room temperature for another 16 hours. Upon completion of the reaction, the solvent was removed under reduced pressure and the residue was chromatographed on silica gel (Petroleum Ether/Ethyl acetate 75/25) to afford 964 mg of the desired product CHA-DA (81% yield). The compound CHA-DA was obtained as a pale yellow solid and the structure of the compound was confirmed by .sup.1H, .sup.13C NMR and HRMS data. .sup.1H NMR (400 MHZ, CDCl.sub.3): 8.17 (d, J=8.7 Hz, 2H), 7.93 (d, J=15.5 Hz, 1H), 7.69 (d, J=8.8 Hz, 2H), 7.45 (d, J=15.5 Hz, 1H), 7.34 (d, J=8.7 Hz, 2H), 6.85 (d, J=8.6 Hz, 2H), 3.19 (s, 6H), 2.72 (t, J=7.5 Hz, 2H), 2.38 (d, J=6.8 Hz, 4H), 1.94-1.87 (m, 2H), 1.65 (dd, J=14.7, 7.2 Hz, 6H), 1.53 (dd, J=14.0, 7.0 Hz, 8H), 1.39 (s, 13H), 1.02 (d, J=6.6 Hz, 3H). .sup.13C NMR (100 MHz, CDCl.sub.3): 189.3, 171.8, 145.5, 141.9, 134.6, 134.5, 130.5, 129.9, 119.0, 117.2, 112.6, 112.5, 65.4, 407, 38.0, 32.0, 29.7, 29.6, 29.4, 29.3, 29.2, 29.0, 28.9, 28.5, 28.4, 25.6, 22.8, 19.3, 14.2.

[0057] HRMS (ESI): calculated for [(C.sub.40H.sub.53NO.sub.3)H] (M+H) 596.4104, measured 596.4088.

Examples 2A-2D (Comparative) and 2E (of the Invention)

Polymerizability of CHA-DA and acid-treated CHA-DA monomers

[0058] CHA-DA monomer of Example 1 was dissolved in chloroform to form a 15 mg/mL solution. 5 L of the CHA-DA solution was drop-casted onto Whatman (grade 1) filter paper (1 cm.sup.2). Then the resultant, yellow-colored film was dried for two minutes and subjected to UV irradiation at 254 nm for one minute (Example 2A), or exposed to saturated acid vapors for one minute, and then UV irradiated at 254 nm for one min (Examples 2B-2E). The action of four acids on the yellow-colored film CHA-DA film was studied (sulfuric acid, nitric acid, trifluoroacetic acid and hydrochloric acidExamples 2B-E, respectively) to evaluate the polymerizability of the acid-treated CHA-DA monomer. The results are tabulated in Table 1 and are shown in FIGS. 1A-1C.

TABLE-US-00001 TABLE 1 Acidic treatment on the yellow- UV irradiation Example colored CHADA casted film 254 nm 2A None No polymerization (comparative) occurred 2B H.sub.2SO.sub.4 vapors; No polymerization (comparative) film retained its yellow color occurred 2C HNO.sub.3 vapors; No polymerization (comparative) film retained its yellow color occurred 2D CF.sub.3COOH vapors; No polymerization (comparative) A colorless film was obtained occurred 2E HCl vapors; Yes, purple-colored (invention) a colorless CHADAHCl CHAPDAHCl film was obtained film

[0059] The results tabulated in Table 1 indicate that neither the chalcone-diacetylene monomer, nor acid-treated chalcone-diacetylene monomers, when the acid was H.sub.2SO.sub.4, HNO.sub.3, and trifluoroacetic acid, underwent UV polymerization to form colored PDA films, apparently due to the bulkiness of the negative counter ions in those acids. In contrast, exposure of the yellow-colored chalcone-diacetylene monomer to HCl vapors resulted in the formation of a colorless film, consisting of the monomer molecules in the protonated form (the ammonium salt), which in turn underwent polymerization, successfully creating the purple colored PDA network, underscoring the key role of the chloride ions in mediating the reorganization of the acid-treated chalcone-diacetylene monomers.

Example 3

Characterization of the CHA-DA-HCl monomer and the corresponding PDA film

[0060] The HCl-reacted monomer (i.e., the colorless CHA-DA-HCl film) and its UV polymerization product (CHA-PDA-HCl film) from Example 2E, were studied by scanning electron microscopy (SEM) and spectroscopic methods.

[0061] SEM images (not shown) of the monomer CHA-DA, the reaction product of the monomer and gaseous HCl, and the UV polymerization product show distinct structural rearrangements of the diacetylenes, following exposure to HCl and subsequent polymerization.

[0062] FIGS. 2A-2C depict the spectroscopic characterization of the HCl-treated chalcone-PDA film, corroborating the structural modulation within the chalcone-diacetylene films accounting for the formation of the polydiacetylene network. The UV-vis spectrum of the initial, yellow-colored chalcone-diacetylene monomer in FIG. 2A features a maximum at around 420 nm accounting for absorption in the violet region and the appearance of the corresponding complementary color yellow of the chalcogen moieties. Following exposure to HCl vapor, this peak completely disappeared, attesting to the blocking of charge transfer within the chalcone residue due to the protonation of the dimethylamine unit. The subsequent UV irradiation (at 254 nm) gave rise to the characteristic peak at around 570 nm of purple-colored PDA.

[0063] The Raman scattering data in FIG. 2B furnished additional evidence for the structural transformations within the chalcone-diacetylene film. Specifically, the Raman spectrum of the chalcone-diacetylene monomer features a prominent band for acetylene (CC) at 2090 cm.sup.1, and a small alkene (CC) peak at 1560 cm.sup.1. After protonation by the action of the gaseous HCl and subsequent UV irradiation, the alkyne band appeared at 2073 cm.sup.1 and alkene (CC) peak at 1454 cm.sup.1 reflecting the formation of the conjugated ene-yne polymer network in the chalcone-PDA film.

[0064] Fourier transform infrared (FTIR) analysis in FIG. 2C complements the UV-vis and Raman spectroscopy experiments, particularly furnishing insight into the supramolecular organization of the chalcone-diacetylene units. Specifically, in the initial yellow-colored chalcone-diacetylene monomer film, the CH stretching region in the FTIR spectrum displays two peaks at 2710 cm.sup.1 and 2805 cm.sup.1, ascribed to aliphatic and aromatic CH stretching peaks, respectively (FIG. 2C, top spectrum). After exposure to HCl vapor, a prominent broad peak appeared at around 3350 cm.sup.1, accounting for the emergence of the protonated NH band (FIG. 2C, middle spectrum). After polymerization, the NH band was red-shifted and slightly reduced in intensity, likely corresponding to the hydrogen bond network contributing to photopolymerization and formation of PDA (FIG. 2C, bottom spectrum).

Example 4

Thermochromism of the CHA-PDA-HCl film

[0065] FIGS. 3A-3C show the thermochromic properties of the HCl-treated chalcone-PDA film that was deposited on filter paper (i.e., of Example 2E).

[0066] At room temperature, the film exhibits a purple color. Colorimetric transformations were recorded upon lowering the temperature below 20 C. (FIG. 3A, top row). A purple-blue transition was apparent even upon cooling the HCl-treated chalcone-PDA film down to 50 C. Notably, all color transitions were reversible, with the HCl-treated chalcone-PDA film showing stability after multiple (e.g. twenty) cooling-warming cycles (20 to 50 C.).

[0067] Different color changes occurred upon exposing the HCl-treated chalcone-PDA film to high temperatures (FIG. 3A, bottom row). Specifically, upon heating to 50 C., the film underwent a reversible purple-orange transition. But further heating to 70 C., produced an irreversible transformation to a yellow-orange color.

[0068] The thermochromic transformations of chalcone-PDA are also manifested in the UV-vis spectroscopy (FIG. 3B) and Raman scattering (FIG. 3C) analyses. Specifically, the prominent visible absorbance peak at around 630 nm with the 580 nm shoulder corresponding to polymerized blue PDA is observed at 50 C. (FIG. 3B). This peak was gradually blue-shifted upon increasing the temperature, reflecting color transformations to purple (at 20 C.) and orange-red at higher temperatures. Importantly, the pronounced chalcone absorbance at 420 nm appears upon heating the film to 70 C., accounting for the occurrence of charge transfer within the chalcone residue upon release of HCl.

[0069] Raman spectroscopy data in FIG. 3C further underscore the molecular transformations associated with the thermochromic properties of HCl-treated chalcone-PDA. Specifically, the band at 2087 cm.sup.1 (corresponding to CC stretching) gradually shifted to a higher frequency at 2115 cm.sup.1, accounting for the thermochromic (blue-to-red) transformations of the film. Raman spectral changes are also apparent in the case of the alkene band at around 1450 cm.sup.1. Specifically, a shoulder at around 1490 cm.sup.1 emerged upon heating from 50 C. to 0 C. (FIG. 3C) reflecting the small conformational change associated with the blue-purple color transition of the PDA system. Further heating of the HCl-treated chalcone-PDA film resulted in the disappearance of the CC peak at 1450 cm.sup.1, and the emergence of the signal at 1500 cm.sup.1 as the predominant spectral feature accounting for the pronounced blue-red PDA transformation.

Example 5

The sensing of NH.SUB.3 .vapor by the CHA-PDA-HCl film

[0070] The goal of the study was to evaluate the detectability of various analytes in the gaseous state by the CHA-PDA-HCl film, i.e., sensing vapors of ammonia vapors and amine compounds.

[0071] FIG. 4A features the pronounced color (top row) and fluorescence (bottom row) transformations of the HCl-treated chalcone-PDA film upon brief exposure to ammonia gas (200 ppm) at 20 C. and at 20 C. At 20 C., ammonia induced a remarkable purple-orange visible transition (FIG. 4A,i top row) and a blue-yellow fluorescence transformation (excitation at 365 nm; FIG. 4A,i bottom row), while at 20 C., the corresponding ammonia-induced visible color and fluorescence were more greenish/brown (FIG. 4A,ii).

[0072] The remarkable optical changes depicted in FIG. 4A are attributed to the removal of the HCl molecules associated with chalcone-PDA, and ammonia-induced structural and associated chromatic transition of the conjugated network of PDA. Both effects are portrayed in the reaction scheme in FIG. 4B. Specifically, scavenging of the acidic proton bound to the dimethylamine groups by ammonia and simultaneous removal of the cognate Cl-ions reintroduce charge transfer from the NMe.sub.2 groups (electron donors) to the carbonyl units (electron acceptors). In parallel, ammonia induced the phase transformation within the conjugated PDA network giving rise to a blue-red transition of PDA. Consequently, a blending of the yellow color of the chalcone residue (due to charge transfer) and red PDA (at 20 C.) gave rise to the dark orange color shown in FIG. 4A,i. Similarly interesting visual transformations were observed in the fluorescence experiments (FIG. 4A,i, bottom). The initial blue appearance reflects the fact that blue-phase PDA is non-fluorescent while the fluorescence of the HCl-treated chalcone is blue. However, following ammonia exposure, the combination of pale-yellow fluorescence of chalcone and red fluorescence of PDA produce the pastel orange color shown in FIG. 4A,i, bottom.

[0073] Exposure of the PDA film to ammonia vapors at 20 C. did not give rise to the blue-red transformation of PDA due to the significantly constrained motion of the conjugated network at that temperature. Accordingly, the visible color at that temperature was dark green, arising from the blending of the yellow color of the chalcone unit and the lavender blue PDA (FIG. 4A,ii, top). Similarly, the greenish-yellow fluorescence induced by ammonia in the HCl-treated chalcone-PDA film is ascribed to the mixing of yellow fluorescence of the chalcone units and the blue-purple emitted fluorescence of the purple phase PDA (FIG. 4A,ii, bottom).

[0074] In comparison with the HCl-treated chalcone-PDA film, the simple PDA film derived from 10,12-tricosadiynoic acid was less reactive towards ammonia vapors and produced only a small color change (blue to purple-blue transition) with a higher concentration of ammonia (1000 ppm) and longer exposure times (five minutes) at ambient temperature.

[0075] FIG. 4C depicts the fluorescence modulation induced upon exposure of the HCl-treated polymerized chalcone-PDA film to ammonia vapor. Fluorescence enhancement after exposure to an analyte was calculated by using the following formula obtained [R. Borah and A. Kumar, Mater. Sci. Eng. C., 2016, 61, 762-772]:

[00002]$\begin{array}{cc}{F}_e=\frac{F_a-F_b}{F_a}100& \begin{array}{c}{F}_e=\mathrm{Fluorescence}\mathrm{enhancement}.\\ F_a=\mathrm{Fluorescence}\mathrm{intensity}\mathrm{after}\mathrm{exposure}.\\ F_b=\mathrm{Fluorescence}\mathrm{intensity}\mathrm{before}\mathrm{exposure}.\end{array}\end{array}$

[0076] The fluorescence emission spectra (excitation 450 nm) in FIG. 4C,i show a significant enhancement of the fluorescence emission, directly dependent upon the concentration of ammonia vapor molecules. Importantly, the calibration curve in FIG. 4C,ii reveals a linear relationship in the range of 0.1-100 ppm, and a detection limit of around 3 ppb (corresponding to experimentally significant 1% fluorescence enhancement), which is on par or better than previously reported ammonia vapor sensors.

[0077] FIG. 4D underlines the selectivity of the HCl-treated chalcone-PDA optical sensor film among different amine vapors. In the experiments, HCl-treated chalcone-PDA films were exposed to the indicated amines 1-7 (at 100 ppm concentration), and the fluorescence emission at 568 nm (excitation 450 nm) was recorded. The fluorescence emission intensity trend in FIG. 4D reflects two parameters contributing in tandem to the optical transformation of the HCl-treated chalcone-PDA film. Specifically, lower PKa values in the case of aniline (1), pyridine (2) and hydrazine (3) likely account for low reactivity (i.e., lesser proton scavenging of the HCl-treated dimethylamine) and concomitant lower fluorescence enhancement (FIG. 4D). In the case of triethylamine (6) and tributylamine (7), the bulky residues likely inhibit proton scavenging capabilities by these two amines, similarly minimizing the fluorescence enhancement effect.

[0078] In comparison, the relatively high pKa of ammonia and methylamine combined with the steric accessibility of the nitrogen electron lone pair in these two molecules afford reactivity and concomitant pronounced fluorescence enhancement induced in the HCl-treated chalcone-PDA. It should also be emphasized, that no color/fluorescence changes for the HCl-treated polymerized chalcone-PDA film were observed after exposure to various organic vapors, including hexane, toluene, DCM, chloroform, THF, DMF, DMSO and EtOH.

Example 6

The Sensing of NH.SUB.3 .Generated by Bacteria with the CHA-PDA-HCl Film

[0079] Ammonia is a prominent volatile metabolite secreted by bacteria. Accordingly, the HCl-treated chalcone-PDA films were tested for visual bacterial sensing (FIGS. 5A-5C). To this end, bacterial strains were cultured in Luria-Bertani (LB) medium at 37 C. Single bacterial colonies from LB agar plates were added to 10 mL of LB broth and maintained at 37 C. for 12h in a shaking incubator (220 rpm). The concentration of bacteria in the medium was determined by measuring the optical density at 600 nm (OD 600). For the sensing experiment, 1.6*106 E. coli bacterial cells in a Luria-Bertani (LB) medium were grown on a Petri dish at a constant temperature (37 C.). The gas emissions from bacteria were monitored by placing a chalcone-PDA deposited paper probe 1 cm above the bacterial solution in a Petri dish (on the cover of the Petri dish). The corresponding color changes from the paper probe were recorded at different time intervals.

[0080] At 37 C., the HCl-treated chalcone-PDA film was initially light-purple but transformed to an orange color within eight hours, accounting for the ammonia gas released by the proliferating bacteria in the LB medium (see FIG. 5A).

[0081] The photographs in FIG. 5B further show the gradual color and fluorescence changes of the HCl-treated chalcone-PDA film. Notably, distinguishable color/fluorescence transformations could be discerned within 3 to 6 hours after initiation of bacterial growth. FIG. 5B also confirms that the control chalcone-PDA film did not undergo chromatic transformations in the presence of LB solution that was not spiked with bacteria. The fluorescence response curve in FIG. 5C (calculated as previously described) further attests to the correlation between the chromatic changes of the film and bacterial proliferation, underscoring the typical exponential growth curve of bacterial populations.

Example 7

The Sensing of Food Spoilage by the CHA-PDA-HCl Film

[0082] The goal of the study was to evaluate the ability of the CHA-PDA-HCl film to monitor food spoilage processes, through the detection of volatile ammonia generated by bacteria proliferating in food products.

[0083] In the food spoilage tests, 10 gm of store-purchased fresh-cut fish (Sparus aurata), chicken and beef were placed in the Petri dish and a paper-deposited chalcone-PDA film was attached to the top cover of the plate. Color and fluorescence monitoring was carried out both at 25 C. (room temperature conditions) and 4 C. (refrigerated conditions).

[0084] The results shown in FIG. 6 indicate that the HCl-treated chalcone-PDA film underwent a pronounced visible purple-orange transformation within 22 hours (fish at room temperature, FIG. 6A,i) or 84 hours (fish at 4 C., FIG. 6A,ii), accounting for bacterial proliferation in the fish sample.

[0085] The time-dependent color and fluorescence photographs of the fish-exposed film in FIG. 6A,ii attest to the feasibility of employing the platform for the HCl-treated chalcone-PDA system for visual monitoring of food spoilage. At room temperature, visual color and fluorescence changes could be discerned already within 16 hours, while after 20 hours a pronounced optical transformation of the film was readily observed, indicating significant bacterial proliferation in the fish sample (FIG. 6A,ii). Importantly, the HCl-treated chalcone-PDA films could be similarly employed for visible monitoring of food spoilage at 4 C. (FIG. 6A,ii, bottom row). Specifically, at 4 0C the color/fluorescence transformations occurred within 48 hours, reflecting the slower proliferation of bacteria at this temperature. Similar color/fluorescence transformations as presented in FIG. 6A were recorded in experiments utilizing beef and chicken.

[0086] To further confirm that the striking visual transformations of the HCl-treated chalcone-PDA films in the food samples (e.g., FIG. 6A) are indeed induced by bacterial contamination, a bacterial spiking experiment was carried out, in which different bacterial concentrations were added to sterilized fish samples (i.e., boiled for 15 minutes) and monitored the color changes of HCl-treated chalcone-PDA films placed above the samples (FIG. 6B). The color photographs in FIG. 6B indeed demonstrate that the purple-orange color change of the HCl-treated chalcone-PDA film was observed earlier in the case of a fish sample spiked with a higher bacterial quantity. Importantly, no color transformation occurred, for the duration of measurement, in the sterilized fish sample to which no bacteria were added.

[0087] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.