Swan probe: A nanoliter-scale and high-throughput sampling interface for coupling electrospray ionization mass...

Mass spectrometry provides a versatile detection method for high-throughput drug screening because it permits the use of native biological substrates and the direct quantification of unlabeled reaction products. This paper describes the design and application of a Swan-shaped probe for high-throughput and nanoliter-scale analysis of biological samples in both a microfluidic droplet array and a multiwell plate with electrospray ionization mass spectrometry (ESI-MS). The Swan probe is fabricated using a single capillary with quite low cost, and it consists of a U-shaped section with a micrometer-sized hole for sampling and a tapered tip for sample electrospray ionization. Continuous sample introduction was carried out under both sampling modes of push-pull and spontaneous injection by sequentially dipping the probe in the sample solutions and then removing them. High-throughput and reliable ESI-MS analysis was achieved in analyzing 256 droplets within 90 min with a peak height RSD of 12.6% (n = 256). To validate its potential in drug discovery, the present system was applied in the screening of inhibitors of acetylcholinesterase (AchE) and the measurement of the IC50 values of identified inhibitors.