Optofluidic lasers are currently of high interest for sensitive intracavity biochemical analysis. In comparison with conventional methods such as fluorescence and colorimetric detection, optofluidic lasers provide a method for amplifying small concentration differences in the gain medium, thus achieving high sensitivity. Here, we report the development of an on-chip ELISA (enzyme-linked immunosorbent assay) laser platform that is able to complete an assay in a short amount of time with small sample/reagent volumes, large dynamic range, and high sensitivity. The arrayed microscale reaction wells in the ELISA lasers can be microfabricated directly on dielectric mirrors, thus significantly improving the quality of the reaction wells and detection reproducibility. The details of the fabrication and characterization of those reaction wells on the mirror are described and the ELISA laser assay protocols are developed. Finally, we applied the ELISA laser to detecting IL-6, showing that a detection limit of about 0.1 pg/mL can be achieved in 1.5 h with 15 μL of sample/reagents per well. This work pushes the ELISA laser a step closer to solving problems in real-world biochemical analysis.
Rapid in situ detection and analysis of trace vapor concentrations at a sub-parts per billion to parts per trillion level remains a challenge for many applications such as indoor air-quality analysis and detection of explosives and narcotics. Micro-gas chromatography (μGC) together with a micro-photoionization detector (μPID) is a prominent method for portable analysis of complex vapor mixtures, but current μPID technology demonstrates poor detection performance compared to benchtop flame ionization detectors (FIDs). This work demonstrates the development of a significantly improved μPID with a sub-picogram detection limit (as low as ∼0.2 pg) comparable to or exceeding that of a benchtop FID, with a large linear dynamic range (>4 orders of magnitude) and robustness (high stability over 200 h of plasma activation). Based on this μPID, a complete μGC–PID system was built and tested on standard sample chromatograms in a laboratory setting to show the system’s analytical capabilities and the detection limit down to sub-parts per trillion concentrations (as low as 0.14 ppt). Practical in-field chromatograms on breath and car exhaust were also generated to demonstrate applicability for in situ experimentation. This work shows that μGC–PID systems can be competitive with traditional GC–FID methods and thus opens a door to rapid trace vapor analysis in the field.
Two-dimensional (2D) gas chromatography (GC) provides enhanced vapor separation capabilities in contrast to conventional one-dimensional GC and is useful for the analysis of highly complex chemical samples. We developed a microfabricated flow-restricted pneumatic modulator (FRPM) for portable comprehensive 2D micro-GC (μGC), which enables rapid 2D injection and separation without compromising the 1D separation speed and eluent peak profiles. 2D injection characteristics such as injection peak width and peak height were fully characterized by using flow-through micro-photoionization detectors (μPIDs) at the FRPM inlet and outlet. A 2D injection peak width of ~25 ms could be achieved with a 2D/1D flow rate ratio over 10. The FRPM was further integrated with a 0.5-m long 2D μcolumn on the same chip, and its performance was characterized. Finally, we developed an automated portable comprehensive 2D μGC consisting of a 10 m OV-1 1D μcolumn, an integrated FRPM with a built-in 0.5 m polyethylene glycol 2D μcolumn, and two μPIDs. Rapid separation of 40 volatile organic compounds in ~5 min was demonstrated. A hybrid 2D contour plot was constructed by using both 1D and 2D chromatograms obtained with the two μPIDs at the end of the 1D and 2D μcolumns, which was enabled by the presence of the flow resistor in the FRPM.
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