Micro-coffee-ring-patterned fiber SERS probes and their in situ detection application in complex liquid environments

Coffee-ring structures, which are easy to prepare, have many hotspots for surface-enhanced Raman scattering (SERS). However, the inhomogeneous distribution of hotspots causes very poor SERS detection reproducibility, which strongly restricts their practical applications. In this paper, by combining a coffee-ring structure with the waveguide effect of optical fibers, we propose novel micro-coffee-ring-patterned fiber SERS probes fabricated by a laboratory-developed laser-induced dynamic dip-coating method. The mechanisms of micro-coffee-ring formation on fiber facet are analyzed in detail. With the help of a programmable dip-coater, micro-coffee-ringpatterned fiber SERS probes can be automatically and reproducibly fabricated, and they simultaneously show high sensitivity and good reproducibility in SERS detections. A detection limit lower than 10(-8) M in aqueous solvent for thiram and methyl parathion (MP) is achieved, and the relative standard deviation (RSD) of the SERS peaks is less than 6%. In addition, benefiting from numerous hotspots provided by micro-coffee rings, this microcoffee-ring-patterned fiber SERS probe presents superior performance in in-situ trace detection of target molecules in complex liquid environments. Detection sensitivities of 10(-7) M for thiram in lake water and in orange juice and 10(-6) M for melamine and tetracycline in liquid milk are achieved.