ABSTRACT
Microϐluidic devices that integrate functional units to perform bioanalytical and diagnostic tests in chips have some unique advantages, such as reducing reagent and sample consumption, and avoiding contamination during sample transfer between analysis procedures. This chapter reviews biosensing techniques that utilize noble metal nanoparticles to develop various spectroscopic methods, including label-free scattering and ϐluorophore-tagged emission methods. Unlike bulk materials such as mirror-like metallic ϐilms, nanoparticles of noble metals, such as gold (Au) and silver (Ag), absorb and scatter the incident light to appear colors, known as localized surface plasmon resonance (LSPR) and also known as particle plasmon resonance (PPR). The resonance frequency of the collective oscillating electrons is dependent on the dielectric properties of the nanoparticles and their surrounding medium. In other words, the binding events of immobilized probes on the particle surfaces will change the scattering frequency sensitively. Also the surface
plasmon induced by the incident light can enhance inelastic Raman scattering of molecules absorbed on noble metal nanoparticles. In addition to act as a substrate to immobilize ϐluorescence labeled molecules, noble metal nanoparticles work as ϐluorescence quenchers or emission enhancement media. When using strong interactions between surface electrons and ϐluorophore dipoles, noble metal nanoparticles can assist Förster resonance energy transfer (FRET) and surface plasmon-coupled emission (SPCE) ϐluorescence detection. Noble metal nanoparticles also have strong light absorbance properties to convert absorbed light to thermal energies, causing detectable refraction index change of surrounding medium to facilitate thermal lens detections. These strong light absorbance properties make noble metal nanoparticles suitable candidates as the sample dispersion matrix to desorb molecules into gas phase and ionize using laser irradiation. The molecules, even proteins, ionized via this photonics mechanism, matrixassisted laser desorption ionization (MALDI), usually remain intact in gas phase. Mass analyzers are able to determine the structures of these large ions. This chapter also reviews applying microϐluidics devices to implement the light absorbance properties of noble metal nanoparticles to develop biosensing methods.
