Chitosan: an integrative biomaterial for lab-on-a-chip devices.

Chitosan is a naturally derived polymer with applications in a variety of industrial and biomedical fields. Recently, it has emerged as a promising material for biological functionalization of microelectromechanical systems (bioMEMS). Due to its unique chemical properties and film forming ability, chitosan serves as a matrix for the assembly of biomolecules, cells, nanoparticles, and other substances. The addition of these components to bioMEMS devices enables them to perform functions such as specific biorecognition, enzymatic catalysis, and controlled drug release. The chitosan film can be integrated in the device by several methods compatible with standard microfabrication technology, including solution casting, spin casting, electrodeposition, and nanoimprinting. This article surveys the usage of chitosan in bioMEMS to date. We discuss the common methods for fabrication, modification, and characterization of chitosan films, and we review a number of demonstrated chitosan-based microdevices. We also highlight the advantages of chitosan over some other functionalization materials for micro-scale devices.

Biofabrication of chitosan-silver composite SERS substrates enabling quantification of adenine by a spectroscopic shift.

Surface-enhanced Raman scattering (SERS) has grown dramatically as an analytical tool for the sensitive and selective detection of molecules adsorbed on nano-roughened noble metal structures. Quantification with SERS based on signal intensity remains challenging due to the complicated fabrication process to obtain well-dispersed nanoparticles and well-ordered substrates. We report a new biofabrication strategy of SERS substrates that enable quantification through a newly discovered spectroscopic shift resulting from the chitosan-analyte interactions in solution. We demonstrate this phenomenon by the quantification of adenine, which is an essential part of the nucleic acid structure and a key component in pathways which generate signal molecules for bacterial communications. The SERS substrates were fabricated simply by sequential electrodeposition of chitosan on patterned gold electrodes and electroplating of a silver nitrate solution through the chitosan scaffold to form a chitosan-silver nanoparticle composite. Active SERS signals of adenine solutions were obtained in real time from the chitosan-silver composite substrates with a significant concentration-dependent spectroscopic shift. The Lorentzian curve fitting of the dominant peaks suggests the presence of two separate peaks with a concentration-dependent area percentage of the separated peaks. The chitosan-mediated composite SERS substrates can be easily biofabricated on predefined electrodes within microfluidic channels for real-time detection in microsystems.

A normal incidence scanning reflectometer of high precision.

A near-normal incidence (~6 degrees ) reflectometer system is described that records continuously and directlythe reflectance R(omega) as a range of photon energies is scanned. The system has an absolute error of +/-2 x 10(-2) and a relative error of +/-2 x 10(-5). It incorporates a quartz light pipe rotating at 70 Hz which captures light from the incident and the reflected beam, respectively, during about 20% of its period of rotation in either case. A gating circuit separates the output signal of the photomultiplier into two channels, corresponding to the incident and the reflected beam, respectively. The signal corresponding to the incident beam is kept constant by a servo system which regulates the gain of the photomultiplier. The reflectance is thus proportional to the signal of the second channel, which is recorded as a function of photon energy. Portions of the reflectance spectrum of Ge are given as examples. No trace of a fine structure in the reflectance of Ge below 2 eV is found.