A Single Silicon Nanowire-Based Ratiometric Biosensor for Ca2+ at Various Locations in a Neuron.

Ionic calcium (Ca2+) is an important second messenger in cells, particularly in the neuron. A deficiency or excess of Ca2+ would lead to neuronal apoptosis and further injury to the brain. For accurate analysis of intracellular Ca2+, a single silicon nanowire (SiNW)-based ratiometric biosensor was constructed by simultaneously anchoring Ru(bpy)2(mcbpy-O-Su-ester)(PF6)2, as a reference molecule, and Fluo-3, as a response molecule, onto the surface of a single SiNW. The SiNW-based biosensor exhibits high sensitivity and favorable selectivity for detecting Ca2+. With the assistance of a micromanipulator and laser scanning confocal microscope, two single SiNW sensors were placed in the body and the neurites of an individual neuron to detect Ca2+. The difference between the concentrations of Ca2+ in the body and neurites was identified. The results from the present study provide new insights into Ca2+ in neurons at a high spatial resolution, and the strategy used in this study provides a new opportunity to investigate cellular metabolism by combining the advantages of a single-cell detection technique and physiology.