Magnetic Micromotors with Spiky Gold Nanoshells as SERS Sensors for Thiram and Bacteria Detection

Surface-enhanced Raman scattering (SERS) is widely used in all kinds of detection due to its ultrahigh sensitivity and selectivity. Micromotors, when used as SERS sensors, or the so-called "hotspots on the fly", can combine both controlled mobility and SERS sensing capacity, and are ideal for versatile in situ detection. In this work, mobile SERS sensors are successfully fabricated by growing gold nanospikes onto magnetic microsphere surfaces. These mobile micromotors can act as normal SERS sensors, characterized by the trace detection of thiram, a highly toxic fungicide. The detection limit can reach 0.1 nM, as good as most other noble metal deposited substrates. With significant magnetic gradient forces, separation of pathogenic bacteria from bulk solution is achieved once these magnetic micromotors bind with bacterial cells. Manipulated propulsion of micromotors, on the other hand, enables them to approach and contact pathogenic bacterial cells on command and further acquire Raman spectra under a controlled degree of contact, a capability never seen with passive sensors. The robotic SERS sensors have demonstrated unique sensing characteristics with controlled manipulations along with discriminative detection between bacterial species. Magnetic beads when modified with spiky gold nanoshells can be used as micromotor SERS sensors for both capture and SERS detection of bacteria. Under the manipulation of an external magnetic field, magnetic micromotors can approach bacterial cells with a controlled degree of contact and the discrimination between E. coli and S. aureus can also be realized from different characteristic Raman spectra peaks. image