Mixing Assisted "Hot Spots" Occupying SERS Strategy for Highly Sensitive In Situ Study.

To solve the problem that analyte molecules cannot easily enter "hot spots" on a conventional solid SERS substrate, we developed a mixing-assisted "hot spots" occupying (MAHSO) SERS strategy to improve utilization of "hot spots". Compared with the conventional substrate, the MAHSO substrate enhances the sensitivity of SERS measurement by thousands of times. The MAHSO substrate possesses excellent properties of high enhancement, high uniformity, and long-term stability because the MAHSO substrate is integrated inside an ultrafast microfluidic mixer. The mixer makes analytes and metal colloid homogeneously mixed, and analytes are naturally located in "hot spots", the gaps between adjacent NPs, during the process that NPs deposit on the channel wall. As a multi-inlet device, the MAHSO chip offers a convenient in situ method to study environmental effects on analytes or molecular interactions by flexibly regulating fluid in microchannels and monitoring responses of analytes by SERS spectra. Because all experiments are conducted in aqueous environments, which is similar to the physiological conditions, the MAHSO chip is especially suitable to be applied to study biomolecules. Using this strategy, different conformational changes of the wild type and mutant G150D of protein PMP22-TM4 depending on environmental pH have been observed in situ and analyzed. As a lab-on-a-chip (LoC) device, the MAHSO SERS chip will benefit the field of molecular dynamics, as well as molecule-molecule or molecule-surface interactions in the future.