Modeling silicon nanostructure surface functionalization for biological detections

As materials scale down to the nano realm with the miniaturization of electronic devices, the surface to volume ratio increases. Consequently, the surface plays the crucial role in nanomaterials. Silicon being the second most abundant element on earth has been exploited in a diverse array of applications, besides the semiconductor industry. For instance, 0-dimensional silicon nanostructures or silicon quantum dots are direct band gap nanomaterials exhibiting photoluminescence (PL) properties due to their tetrahedral crystalline structure. Its PL characteristic is utilizable in bio-sensory applications such as detection of cancer cells and several biological molecules of medical importance. The structures of the silicon quantum dots can be terminated by several possible passivants, such as chemical, bio-chemical or biological molecules, for the retention of its tetrahedral symmetry. In order to realize the practical applications of the silicon quantum dots, its PL characteristic needs to be efficiently held in different media encountered in its practical applications. The recent advances in the understanding of structure-property relationship of various chemically and biologically functionalized silicon quantum dots based on our computational investigations at the quantum-mechanical level and their profound implications for bio-sensory applications are reviewed in this article. Surface functionalization is an essential step in the actualization of the silicon quantum dots (SiQDs) as biological nanoprobes and sensors. Capping SiQDs with the alkyl group induces minimal changes in the optical spectra with respect to its hydrogen passivated counterpart, while covering the surface with NH₂, SH, and OH results in discernible changes in its PL properties. Varying the S coverage on the surface can further tune the optical properties of SiQDs. SiQDs with the above functionalization have shown excellent applications in chemical and biological sensing.