Detection device and methods of use

Abstract

An imaging system for exciting and measuring fluorescence on or in samples comprising fluorescent materials (e.g. fluorescent labels, dyes or pigments). In one embodiment, a device is used to detect fluorescent labels on nucleic acid. In a preferred embodiment, the device is configured such that fluorescent labels in a plurality of different DNA templates are simultaneously detected.

Claims

1. A method of imaging fluorescent signals, comprising: a) providing i) a first array in a first flow cell, said first array comprising a plurality of different nucleic acid templates, ii) a second array in a second flow cell, said second array comprising a plurality of different nucleic acid templates, said first and second flow cells positioned on a moving support, iii) nucleic acid sequencing reagents capable of producing fluorescent signals from fluorescent labels covalently attached to a nucleotide that can be incorporated in said nucleic acid, and iv) a single camera, wherein said first and second flow cells comprise a fluid channel and said nucleic acid templates are arrayed on said fluid channel, said fluid channel in fluidic communication with a side entrance port; b) introducing nucleic acid sequencing reagents into said first flow cell via said side entrance port under conditions so as to generate first fluorescent signals in said first array; c) introducing nucleic acid sequencing reagents into said second flow cell via said side entrance port under conditions such that, while said second array in said second flow cell is undergoing one or more reaction steps so as to produce fluorescent signals, said first array is being imaged with said single camera; d) moving said first flow cell on said moving support; and e) moving said second flow cell on said moving support and imaging said second array in said second flow cell with said single camera.

2. The method of claim 1, wherein said moving support is a rotary stage.

3. The method of claim 1, further comprising f) draining said fluid channel of said first flow cell at least in part by gravity.

4. The method of claim 1, wherein reagent and buffer reservoirs are in communication with said first and second flow cells via said side entrance port.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 schematically shows one embodiment of the imaging system of the present invention, said embodiment comprising a) a circular array of LEDs configured such that the emitted light converges on a region or platform (e.g. a position for a sample, flow cell, etc.) so as to excite fluorescence of fluorescent material, b) a lens assembly positioned above the region so as to capture at least a portion of said fluorescence, c) a filter wheel comprising bandpass filters, and d) light collection means (in this case a cooled CCD camera), wherein said filter wheel is positioned between the region where the light converges and the light collection means.

(2) FIGS. 2A-B schematically show one embodiment of a flow cell. FIG. 2A shows a three dimensional translucent view of a flow cell, comprising fluid tubing connections, cartride heaters, and O-ring seal. FIG. 2B is a two dimensional drawing of a side view of a flow cell, showing an array or slide with spaced spots on the surface (representing positions for biomolecules and/or anchoring molecules), said array positioned in a fluid channel such that solutions of buffers and/or reagents can be introduced over the surface under conditions whereby reactions and/or washing can be achieved. The arrows show one preferred direction of fluid flow, with entrance and exit ports, as well as one preferred method of sealing (O-ring seal).

(3) FIG. 3 schematically shows one embodiment of a fluidics system, comprising a variety of illustrative reagent and buffer reservoirs in communication (via tubing or other channeling into a manifold comprising valves) with one embodiment of a flow cell (comprising a side entrance port and one or more heaters), wherein the array or chip is inverted and the exit port is on the bottom, thereby permitting the fluid channel to be drained at least in part by gravity so that waste can be readily collected into a reservoir.

(4) FIG. 4A schematically shows another embodiment of an imaging system, wherein two flow cells and two cameras are employed to increase capacity and efficiency (e.g. while one chip in a first flow cell is undergoing one or more reaction steps, a second chip in a second flow cell is being scanned and imaged). FIG. 4B shows a closer illustration of the three piece lens system, including the two pair color filters and dichroic beam splitters.

(5) FIGS. 5A-5D show an illustrative excitation and emission filter selection (grey rectangles) for four illustrative dyes, relative to the dye's excitation (dashed) and emission (solid) spectra. FIG. 5A shows the excitation and emission filter selection for the dye BODIPY FL. FIG. 5B shows the excitation and emission filter selection for the dye R6G. FIG. 5C shows the excitation and emission filter selection for the dye ROX. FIG. 5D shows the excitation and emission filter selection for the dye BODIPY 650.

(6) FIGS. 6A-6B show the raw data (FIG. 6A) and crosstalk adjusted data (FIG. 6B) for four illustrative dyes.

DETAILED DESCRIPTION

(7) The present invention contemplates a fluorescent detection system and a flow cell for processing biomolecules (e.g. nucleic acid samples) arrayed on a “chip” or other surface (e.g. microscope slide, etc.). The flow cell permits the user to perform biological reactions, including but not limited to, hybridization and sequencing of nucleic acids.

(8) It is not intended that the present invention be limited to particular light sources. By way of example only, the system can employ ultra-bright LEDs (such as those available from Philips Lumileds Lighting Co., San Jose, Calif.) of different colors to excite dyes attached to the arrayed nucleic acids. These LEDs are more cost effective and longer life than conventionally used gas or solid state lasers. Other non-lasing sources of lights such as incandescent or fluorescent lamps may also be used.

(9) FIG. 1 shows a useful configuration of the LEDs, whereby the emitted light converges on a region or platform (e.g. suitable for positioning the flow cell or sample). However, linear arrays of LEDs can also be used.

(10) It is not intended that the present invention be limited to particular light collection devices. By way of example only, the system may employ a high sensitivity CCD camera (such as those available from Roper Scientific, Inc., Photometric division, Tucson Ariz. or those available from Apogee Instruments, Roseville, Calif.) to image the fluorescent dyes and make measurements of their intensity. The CCD cameras may also be cooled to increase their sensitivity to low noise level signals. These may also be CMOS, vidicon or other types of electronic camera systems.

(11) Since LED illumination light is not a collimated beam as from lasers, it is therefore an appropriate choice for imaging a larger area of many nucleic acid spots. To get sufficient light and therefore fluorescent signals over the larger area, the area seen by each pixel of the camera must be of sufficient size to allow enough fluorescent dye molecules to create a sufficient signal (for example, an Apogee U13 CCD available has 1.3 megapixels of 16 microns in size, while the Apogee U32 has 3.2 megapixels of 6.8 microns in size).

(12) To increase capacity and efficiency, the present invention contemplates in one embodiment, a two flow cell system (e.g. while one chip in a first flow cell is undergoing one or more reaction steps, a second chip in a second flow cell is being scanned and imaged) with a single camera. In yet another embodiment of an imaging system, two flow cells and two cameras are employed (FIG. 4A and shown as a close up in FIG. 4B).

(13) In one embodiment, the chip containing the array of nucleic acid spots is processed in a transparent flow cell incorporated within the instrument, which flows reagent past the spots and produces the signals required for sequencing (see FIGS. 2A and 2B). In a preferred embodiment, the chip remains in the flow cell while it is imaged by the LED detector. The flow cell and associated reagents adds the nucleic acids, enzymes, buffers, etc. that are required to produce the fluorescent signals required for each sequencing step, then the flow cell delivered the required reagents to remove the fluorescent signals in preparation for the next cycle. Measurement by the detector occurs between these two steps. In order for reactions to take place, the flow channels need to be of sufficient dimensions. For example, the channel by the array should be at least 0.1 mm in depth (more preferably 0.5 mm in depth) and the volume formed by the chip, the block and the seal should be at least 100 microliters in volume (more preferably, between 100 and 700 microliters, and still more preferably, between 150 and 300 microliters, e.g. 200 microliters, in volume).

(14) The flow cell is preferably motionless (i.e. not moved during reactions or imaging). On the other hand, the flow cell can readily be mounted on a rotary or one or more linear stages, permitting movement. For example, in a two flow cell embodiment, the two flow cells may move up and down (or side to side) across the imaging system. Movement may be desired where additional processes are desired (e.g. where exposure to UV light is desired for photochemical reactions within the flow cell, such as removal of photocleavable fluorescent labels), when multiple flow cells share a single camera, or when the field of view of the detection system is smaller than the desired area to be measured on the flow cell. The detector system may also be moved instead of the flow cell.

(15) The flow cell is preferably in fluid communication with a fluidics system (see illustrative system shown in FIG. 3. In one embodiment, each bottle is pressurized with a small positive gas pressure. Opening the appropriate valve allows reagent to flow from the source bottle through the flow cell to the appropriate collection vessel(s). In one embodiment, the nucleotides and polymerase solutions will be recovered in a separate collection bottle for re-use in a subsequent cycle. In one embodiment, hazardous waste will be recovered in a separate collection bottle. The bottle and valve configuration allow the wash fluid to flush the entire valve train for the system as well as the flow cell. In one embodiment, the process steps comprise: 1) flushing the system with wash reagent, 2) introducing nucleotides (e.g. flowing a nucleotide cocktail) and polymerase, 3) flushing the system with wash reagent, 4) introducing de-blocking reagent (enzyme or compounds capable of removing protective groups in order to permit nucleic acid extension by a polymerase), 5) image, 6) introduce label removing reagent (enzyme or compounds capable of removing fluorescent labels), and 7) flushing the system with wash reagent.

(16) The system can be made to include a user interface system. The Labview (National Instruments, Austin, Tex.) system is available and provides relatively simply software for computer controlled systems. Galil Motion Control (Rocklin, Calif.) provides motion control systems that can be interfaced to control the instrument.

EXAMPLE

(17) Method for removing crosstalk between detected fluorescent signals for a multicolor system. Previous sequencing systems utilizing lasers have attempted to minimize the number of lasers in order to reduce costs (for example ABI Prism sequencers). For a four color detection system using LEDs, the light sources are fairly inexpensive and it is desirable to have four separate color light sources in order to reduce crosstalk between colors as follows.

(18) To determine actual fluorescent intensities for the four colors, A, B, C and D from measured detector outputs, M.sub.A, M.sub.B, M.sub.C, M.sub.D in corresponding channels, you need to know all of the crosstalk factors: R.sub.AB, R.sub.BA, R.sub.BC, R.sub.CB, R.sub.CD, R.sub.DC. Six crosstalk factors are used for illustrative purposes. There may be more or fewer factors which may be incorporated into the analysis.

(19) For example, R.sub.AB is the ratio between the portion of the signal in the A channel coming from the B dye and the actual intensity of the B dye. If for instance R.sub.AB is 20%, then the A channel will have an additional signal equal to 0.2 times the actual B dye intensity in the B channel. Thus for channel B, the observed measurement, M.sub.B, is the direct measurement of B and the two contributions from the adjacent channels (if any):
M.sub.B=B+R.sub.BAA+R.sub.BCC  (1)
For the four channels, this may be written in matrix form:

(20) $\begin{array}{cc}\left[\begin{array}{c}{M}_A\\ M_B\\ M_C\\ M_D\end{array}\right]=K\left[\begin{array}{c}A\\ B\\ C\\ D\end{array}\right]\mathrm{where}K=\left[\begin{array}{cccc}1& R_{\mathrm{AB}}& 0& 0\\ R_{\mathrm{BA}}& 1& R_{\mathrm{BC}}& 0\\ 0& R_{\mathrm{CB}}& 1& R_{\mathrm{CD}}\\ 0& 0& R_{\mathrm{DC}}& 1\end{array}\right].& \left(2\right)\end{array}$
Each of the six crosstalk factors may be determined through a simple experiment with pure dyes. Some may be zero and they might vary with intensity, so we may need a table of a number of values for each depending on the measured intensity range. We want to solve for the actual fluorescent signals, A, B, C and D given the detector measurements, M.sub.A, M.sub.B, M.sub.C, M.sub.D. Thus, we want to solve the above matrix equation (2). This is:

(21) $\begin{array}{cc}\left[\begin{array}{c}A\\ B\\ C\\ D\end{array}\right]=K^{-1}\left[\begin{array}{c}{M}_A\\ M_B\\ M_C\\ M_D\end{array}\right]& \left(3\right)\end{array}$
where K.sup.−1 is the inverse of matrix K. Although this may be written out in terms of the six crosstalk factors, it is somewhat complex and is best performed by plugging in the numbers and letting the computer take the inverse. FIG. 6 shows the raw data (6A) and crosstalk adjusted data (6B) for four illustrative dyes.