Chemical sensors based on nanoparticle arrays

The size-dependent properties of nanomaterials are currently attracting a great deal of interest in the research community because of the many important potential applications in microelectronic, data storage and sensing devices. The signature optical property of metal nanoparticles is the localized surface plasmon resonance (LSPR), which occurs when collective oscillations of the conduction electrons are excited by light. The LSPR results in wavelength-selective photon absorption, scattering and local electromagnetic field enhancement. The latter contributes to the significant enhancements observed in surface-enhanced Raman scattering (SERS) and other surface-enhanced spectroscopies. Several groups have already demonstrated the enormous potential of compact, integrated SERS sensors for a broad range of chemical and biological sensing applications. However, the systems described so far have generally utilized substrates with a wide range of feature sizes and irregular spatial distributions. These factors contribute to relatively poor reproducibility between sensors. Fabrication techniques based on ordered, self-assembled arrays of nanospheres appear to offer a convenient and inexpensive means for generating uniform structures. Progress in applying these methods to the fabrication of reproducible SERS microsensors will be described.