Surface-enhanced Resonance Raman Spectroscopy Signals Research Articles

Magnetic field enriched surface enhanced resonance Raman spectroscopy for early malaria diagnosis

Hemozoin is a by-product of malaria infection in erythrocytes, which has been explored as a biomarker for early malaria diagnosis. We report magnetic field-enriched surface-enhanced resonance Raman spectroscopy (SERRS) of β-hematin crystals, which are the equivalent of hemozoin biocrystals in spectroscopic features, by using magnetic nanoparticles with iron oxide core and silver shell (Fe(3)O(4)@Ag). The external magnetic field enriches β-hematin crystals and enhances the binding between β-hematin crystals and magnetic nanoparticles, which provides further improvement in SERRS signals. The magnetic field-enriched SERRS signal of β-hematin crystals shows approximately five orders of magnitude enhancement in the resonance Raman signal, in comparison to about three orders of magnitude improvement in the SERRS signal without the influence of magnetic field. The improvement has led to a β-hematin detection limit at a concentration of 5 nM (roughly equivalent to 30 parasites/μl at the early stages of malaria infection), which demonstrates the potential of magnetic field-enriched SERRS technique in early malaria diagnosis.

Plasmonic Split-Ring Resonators as Dichroic Nanophotonic DNA Biosensors

Surface enhanced resonance Raman spectroscopy (SERRS) is a powerful molecular sensing tool that can be applied to a number of applications in the field of molecular diagnostics. We demonstrate that by using electron beam lithography to manipulate the nanoscale geometry of Ag split-ring resonators we can tune their optical properties such that they exhibit two independently addressable high frequency plasmon resonance modes for SERRS. This tailored multimodal, polarization dependent activity enables the split rings to act as discriminating sensors, with each resonance tuned for a particular sensing purpose. The structures are used as multiwavelength, multianalyte DNA SERRS sensors, with each resonance tuned to both the absorption wavelength of a differently colored Raman reporter molecule and its corresponding laser excitation wavelength. The ability of each resonance to independently sense small concentrations of a single DNA type from within a mixed population is demonstrated. Also shown is the effect of the split ring's dichroic response on the SERRS signal and the sensor's limit of detection of each resonance mode (switching its sensory reaction "on" and "off" depending on the orientation of the exciting light).

The influence of pH and anions on the adsorption mechanism of rifampicin on silver colloids

AbstractThe influence of pH and anions on the adsorption mechanism of rifampicin on colloidal silver nanoparticles has been analysed by electronic absorption, resonance Raman (RR) and surface‐enhanced resonance Raman spectroscopy (SERRS). Rifampicin is a widely used antibiotic with a zwitterionic nature. SERRS spectra of rifampicin adsorbed on silver sols, prepared using hydroxylamine hydrochloride as reducing agent, undergo dramatic changes upon lowering the pH. The spectral form changes progressively from that characteristic of chemisorbed rifampicin (at pH > 7) to one very similar to the rifampicin RR spectrum (at lower pH), indicative of a modification of the adsorption mechanism on the surface of the Ag nanoparticles. The RR‐type SERRS spectrum is proposed to result from formation of an ion pair between rifampicin and Cl− anions, which, deriving from the colloid preparation, are adsorbed on the Ag surface. The addition of anions to the hydroxylamine hydrochloride sol facilitates conversion from the chemisorbed to ion pair form and leads to an order of magnitude increase in the SERRS signal. Copyright © 2007 John Wiley & Sons, Ltd.