Attomolar Sensing Based on Liquid-Interface Assisted Surface Enhanced Raman Scattering in Microfluidic Chip by Femtosecond Laser Processing.

Surface enhanced Raman scattering (SERS) is a multidisciplinary trace analysis technique based on plasmonic effects. The development of SERS microfluidic chips has been exploited extensively in recent times impacting on applications in diverse fields. However, despite much progress, the excitation of label-free molecule is extremely challenging when analyte concentrations are lower than 1 nM due to the blinking SERS effect. In this paper, a novel analytical strategy which can achieve detection limits at aM level is proposed. This performance improvement is due to the use of a glass microfluidic chip that features an analyte air-solution interface which forms on the SERS substrate in the microfluidic channel, whereby the analyte molecules aggregate locally at the interface during the measurements, hence the term liquid-interface assisted SERS (LI-SERS). The microfluidic chips are fabricated using hybrid femtosecond laser processing consisting of femtosecond laser assisted chemical etching, selective metallization and metal surface nanostructuring. The novel LI-SERS technique can achieves an analytical enhancement factor of 1.5 × 1014 providing a detection limit below 10-17 M (<10 aM). The mechanism for the extraordinary enhancement afforded by LI-SERS is attributed to Marangoni convection induced by the photothermal effect.