Nature Commun. 5, 3779 (2014)

Enzyme-linked immunosorbent assay (ELISA) is a well-known technique for biomolecular analysis. Xiang Wu and a team from the University of Michigan (USA), Fudan University (China) and the University of Texas (USA) have now demonstrated that using an optofluidic laser can aid ELISA tests. This technique is particularly interesting because the ELISA occurs inside the laser cavity. The laser is pumped by a pulsed optical parametric oscillator (wavelength, 535 nm; pulse width, 5 ns; repetition rate, 20 Hz; threshold; ∼320 μJ mm−2). The laser turn-on time is used as the sensing signal; it is inversely proportional to the enzyme concentration and hence also to the analyte concentration in the cavity. The optofluidic laser-based ELISA test has the advantage that it can better isolate the ELISA signal from background signals, such as excitation light leakage. The team demonstrated the utility of the concept by the dual-mode detection of interleukin-6 using commercial ELISA kits. In this comparison, sensing signals were simultaneously detected by the optofluidic laser-based ELISA and by conventional ELISA. The new technique had a detection limit of 1 fg ml−1 (38 aM) and a dynamic range of six orders of magnitude, whereas the conventional ELISA results became unreliable below a concentration of ∼10 fg ml−1.