Portable SERS-enabled micropipettes for microarea sampling and reliably quantitative detection of surface organic residues.

We report the first microsampling device for reliably quantitative, label-free and separation-free detection of multicomponents of surface organic residues (SORs) by means of a quality controllable surface-enhanced Raman scattering (SERS)-enabled micropipette. The micropipette is comprised of a drawn glass capillary with a tiny orifice (∼50 μm) at the distal tip, where the specially designed nanorattles (NRs) are compactly coated on the inner wall surface. SERS signals of 4-mercapto benzoic acid (MBA) anchored inside the internal gap of NRs could be used to evaluate and control the quality of micropipettes and, therefore, allow us to overcome the limitations of a reliably quantitative SERS assay using traditional substrates without an internal standard. By dropping a trace extraction agent on targeting SORs located on a narrow surface, the capillary and SERS functionalities of these micropipettes allow on-site microsampling via capillary action and subsequent multiplex distinction/detection due to their molecularly narrow Raman peaks. For example, 8 nM thiram (TMTD), 8 nM malachite green (MG), and 1.5 μM (400 ppb) methyl parathion (MPT) on pepper and cucumber peels have been simultaneously detected in a wide detection range. The portable SERS-enabled device could potentially be facilely incorporated with liquid-liquid or solid phase micro-extracting devices for a broader range of applications in rapid and field analysis of food/public/environment security related SORs.