This paper demonstrates the experimental results of combining new state-of-the-art Geiger mode avalanche photodiodes with an integrated hybrid active/passive quenching circuit. This creates an ultra-compact form factor for a low-light level detection module. Both devices, the photodiode and the quenching circuit, are fabricated using conventional CMOS process technology and wafer substrates. The photodiodes operate at low voltage levels (30 V to 40V). Detector active areas are of various dimensions (10μm to 50μm) and shapes (circular, cylindrical or square). The integrated active/passive quenching circuit is included on a 2.5 mm × 2.5 mm die, which has the functionalities of bias conditioning, passive/active quench, output signal generation and active recharge. The prototypes are hybrid packaged onto a PCB substrate. The module is characterised for detecting very low level optical signals such as the single photon activities. Parameters such as dark counts, timing jitter, and responsivity will be shown for the compact detection module. Our findings show that the proposed avalanche photodiode operation is considerably faster than the conventional discrete systems and the module size is greatly reduced.
For future fully integrated sensing applications, a CMOS sensor will be required. New CMOS photon counting sensors have recently become available and these devices provide high quantum efficiency, photon counting sensitivity, low power and new devices in arrays and with on-chip electronics. In biological applications, photon counting is focused on the detection of low intensity fluorescence signals from fluorophores conjugated to proteins or nucleic acid biomarkers
from fluorescent proteins. We describe the development of a novel microtitre plate reader format, or bioassay platform that incorporates arrays of photon counting detectors for multiple parallel readout and data acquisition. Using Pyrex wafers, we have designed and fabricated custom-made reaction wells using Pyrex and deep ion trench etched silicon, which produce optically clear structures to facilitate fluorescence detection in biological samples volumes of 2 nL to 2 μL. For initial verification of the system, a new photon counting detector from SensL is used to determine the effectiveness of the wells as the bioassay platform. The compact unit consists of a fibre coupled silicon photon counting sensor, thermoelectric cooler, thermoelectric controller, active quenching circuit, power supplies, and an USB interface to the operating software. Included in the module is a counter with time binning capability. Sensitivity increases of more than two orders of magnitude in fluorescence detection are expected over commercially available instruments. This system demonstrates that a miniaturized, low cost solution is possible for fluorescence bioassay detection, which can be used to meet growing demands in the in vitro diagnostics and Point of Care markets.
There is a need for low cost, miniature, integrated optical systems for bioassay monitoring to meet the growing in vitro and point-of-care diagnostics markets. To this end, we are investigating the use of silicon photomultipliers (SiPM) as device upon which to base our technology development. SiPMs have been used successfully in many high-energy physics applications, but their application as a fully integrated biological detection platform has not been shown. In this paper we will present a new detection platform for the measurement of fluorescent biomolecules at much lower concentrations than commercially available systems. Our results show approaches that demonstrate the use of SiPM for the detection of fluorescent proteins and fluorescent-labelled DNA sequences. The SiPM and sample platforms are integrated so that the minimum distance separating the detector from the sample is realised. In addition, direct immobilisation of the DNA sequences onto the SiPM surface is achieved. This combined approach shows improved sensitivities for both the fluorescent proteins and fluorescent-labelled DNA.
We are presenting results that show the use of SiPM as a successful technology for the measurement of fluorescent biomolecules at improved lower concentrations.
The design of a 4 × 1 photon-counting avalanche photodiode array with fully integrated active bias controlling circuit is presented in this paper. The array uses highly sensitive Geiger mode avalanche photodiodes and is capable of detecting four single-photon-level optical signals simultaneously. The photodiode pixels can work either in parallel mode or independently because of the separate gate configuration. The photodiodes are fabricated using a CMOS compatible process with the integrated active quenching and recharging circuit manufactured via 1.5μm CMOS process. The whole system is included on a 2.5mm × 2.5mm die. Simulations show that the fully functional system can detect single photons at up to 20MHz with each pixel or 80MHz with all channels.