Portable high gain fluorescence detection system

Abstract

An instrument for fluorometric assays in liquid samples is disclosed. The instrument may include multiple optical channels for monitoring a first fluorophore associated with a target analyte and a second fluorophore associated with a control. The disclosed instrument finds utility in any number of applications, including microfluidic molecular biological assays based on PCR amplification of target nucleic acids and fluorometric assays in general.

1 - 36 . (canceled) 
     
     
         37 . An apparatus for performing a fluorescence assay on a sample contained in a detection chamber of a microassay cartridge, the apparatus comprising:
 a) a housing configured for receiving the microassay cartridge, the housing comprising a host controller with clock, memory and firmware, and a scanning detector head, wherein the scanning detector head is configured to move in a series of spatially resolved steps over the detection chamber according to instructions executed by the host controller, the scanning detector head comprising:
 i) one or more optical channels, each optical channel having an excitation light source, an objective lens for directing the excitation light onto the sample and for receiving fluorescence emissions therefrom, an emissions sensor for detecting the fluorescence emissions, and an amplifier circuit operatively connected to the emissions sensor, wherein the amplifier circuit is enabled to amplify a voltage from the sensor, thereby generating an amplified voltage signal output; 
 ii) an embedded microprocessor with clock, memory, and firmware for performing a scan of the microassay cartridge while the scanning detector head is moving in the series of steps under control of the host controller, the embedded microprocessor having an electronic input for receiving the amplifier output, wherein the embedded microprocessor is enabled to digitally process the amplifier voltage signal output at each step of the scan across the detection chamber; 
   b) further wherein the embedded microprocessor generates a digital output comprising digitally processed data collected during the scan and conveys the digital output to the host controller; and   c) further wherein the embedded microprocessor is configured to compare the amplified voltage signal output with a threshold value and score the signal as a digital one if greater than the threshold value and as a digital zero if less than the threshold value for each step in the scan, and the digital output is a string of single-bit digital scores for each step in the scan.   
     
     
         38 . The apparatus of  claim 37 , wherein the host controller is provided with instructions to receive the digital output from the embedded microprocessor and to process the digital output to generate an assay result, and wherein the apparatus is further provided with a user interface for displaying or electronically transmitting the assay result. 
     
     
         39 . The apparatus of  claim 38 , wherein the host controller reports a qualitative assay result for detection of a target analyte in the sample. 
     
     
         40 . The apparatus of  claim 37 , wherein the scanning detector head is operatively driven in a series of linear steps by a stepper motor under control of the host controller while scanning the detection chamber with spatial resolution under control of the embedded microprocessor. 
     
     
         41 . The apparatus of  claim 37 , wherein the embedded microprocessor is configured for strobing the excitation light source at a strobe rate and with a selectable pulse width configured to filter electrical or ambient interference. 
     
     
         42 . The apparatus of  claim 37 , wherein the sensor and amplifier circuit form a low noise three-stage amplifier circuit surrounded by a faraday cage. 
     
     
         43 . The apparatus of  claim 42 , wherein the three-stage amplifier circuit is electronically shielded from electronic noise originating outside the scanning detector head. 
     
     
         44 . The apparatus of  claim 42 , wherein excitation electronics and emission electronics are separately grounded in the scanning detector head. 
     
     
         45 . The apparatus of  claim 37 , wherein the excitation light source is a spectrally specific LED configured with excitation filter for transitioning an essentially monochromatic excitation beam onto the detection chamber. 
     
     
         46 . The apparatus of  claim 45 , wherein the LED is a surface mounted LED. 
     
     
         47 . The apparatus of  claim 37 , wherein the emissions sensor is a photodiode, a CCD chip, a CMOS chip, a photomultiplier, an avalanche diode, or a photosensitive electronic device. 
     
     
         48 . The apparatus of  claim 39 , wherein the fluorescence assay is an assay for a nucleic acid target or a protein target in the sample. 
     
     
         49 . A method for reducing noise during fluorescence assay of a liquid sample, the method comprising digitally processing a signal output at each step of a scan of the sample, wherein the signal output is compared to a threshold value and scored as a digital one if greater than the threshold value and as a digital zero if less than the threshold value for each step in the scan. 
     
     
         50 . The method of  claim 49 , wherein the digital output is a string of single-bit scores for each step in the scan. 
     
     
         51 . The method of  claim 49 , wherein the digital output comprises the sum of all the scores for all steps in the scan. 
     
     
         52 . The method of  claim 49 , wherein the digital output is a single-bit digital score, a string of single-bit digital scores, or a calculation based on the single-bit digital scores.