Polymer-modified microfluidic immunochip for enhanced electrochemical detection of troponin I

We report enhanced electrochemical detection of a cardiac biomarker using a combination of a disposable microfluidic immunochip fabricated in Vacrel® 8100 photoresist film and a highly effective surface functionalization employing polyethylenimine (PEI). The use of the photoresist film enables fast prototyping and low-cost production without the need for a cleanroom. We use the surface carboxylates of the photoresist to biofunctionalize the microchannel on the chip using direct amine-specific coupling and modification via adsorbed and immobilized PEI in both linear (LPEI) and branched (BPEI) form. Characteristics of each immobilization strategy are assessed by a sandwich immunoassay for troponin I quantification in serum. The best assay performance is achieved using the immunochip modified with immobilized BPEI: the antigen was routinely detected at concentrations of 25 pg ml−1 in 4 min read-out time and 5 μl serum sample, representing an 18-fold improvement of the detection limit and 2.5-times faster read-out time in comparison to the assay implemented over amine-reactive esters without the PEI coating. We demonstrate that immobilized BPEI represents a stable and tunable scaffold that enhances biomolecule immobilization up to 60-times and stability 2-fold while lowering non-specific binding by factor of three. This system provides a versatile and nonaggressive means for incorporation of biological material to virtually any platform design.