Heterogeneous immunoassays in microfluidic format using fluorescence detection with integrated amorphous silicon photodiodes

Abstract

Miniaturization of immunoassays through microfluidic technology has the potential to decrease the time and the quantity of reactants required for analysis, together with the potential of achieving multiplexing and portability. A lab-on-chip system incorporating a thin-film amorphous silicon (a-Si:H) photodiode microfabricated on a glass substrate with a thin-film amorphous silicon-carbon alloy directly deposited above the photodiode and acting as a fluorescence filter is integrated with a polydimethylsiloxane-based microfluidic network for the direct detection of antibody-antigen molecular recognition reactions using fluorescence. The model immunoassay used consists of primary antibody adsorption to the microchannel walls followed by its recognition by a secondary antibody labeled with a fluorescent quantum-dot tag. The conditions for the flow-through analysis in the microfluidic format were defined and the total assay time was 30 min. Specific molecular recognition was quantitatively detected. The measurements made with the a-Si:H photodiode are consistent with that obtained with a fluorescence microscope and both show a linear dependence on the antibody concentration in the nanomolar-micromolar range.

Serological and molecular rapid diagnostic tests for Toxoplasma infection in humans and animals

“…The incorporation of chitosan-coated zinc oxide nanoparticles into the microfluidic channel improved the sensitivity as well as simplified the operating procedure by reducing the analysis time to 31 min [87]. Attempts have been made to exploit the potential POC benefits of microfluidics by miniaturizing and integrating the optical elements, including using amorphous silicon photodiodes [88] and optical fiber light guides [89]. A POC device based on LIF microfluidics has the potential to decrease the time and quantity of reactants for analysis, along with multiplexing and portability [84].…”

Surface modification for PDMS‐based microfluidic devices

“…Compared to silicon and glass based microfluidic devices, PDMS‐based microfluidics does not suffer from the same practical and financial barriers to prototype fabrication. In addition to the favorable optical and mechanical properties of the bulk material, the biocompatibility of surface‐modified PDMS allows microfluidic bio‐applications such as separation of biomolecules 16, 20, 33, 48, 53, 89, and immuno‐ 30, 31, 90 and cell‐based assays 17, 80.…”

“…Mouse IgG has been successfully detected in modified PDMS microchannels with adsorbed IgG 90 or multilayers of IgG incorporated into polyelectrolyte layers 31. A comparison of these two layers showed a much lower detection limit (6.7 pM) for the IgG multilayers 31, although a shorter assay time (30 min) was observed in the case of monolayer IgG adsorption 90. Sung et al 30 covalently immobilized protein G on a PDMS microchannel via the combination of LBL‐ and UV‐induced graft polymerization techniques.…”

Organic Photodetectors in Analytical Applications

“…Numerous studies have been reported on peroxyoxalate CL (POCL) sensors for monitoring H2O2 with a PMT [36][37][38] or a silicon photodiode [39][40][41]. Hoffman et al showed [42] that these POCL sensors can be further miniaturized by successfully integrating an organic copper phthalocyanine/fullerene(CuPc/C60) based OPD with PDMS microchannels.…”