On-line SERS detection of single bacterium using novel SERS nanoprobes and a microfluidic dielectrophoresis device.

The integration of novel surface-enhanced Raman scattering (SERS) nanoprobes and a microfluidic dielectrophoresis (DEP) device is developed for rapid on-line SERS detection of Salmonella enterica serotype Choleraesuis and Neisseria lactamica. The SERS nanoprobes are prepared by immobilization of specific antibody onto the surface of nanoaggregate-embedded beads (NAEBs), which are silica-coated, dye-induced aggregates of a small number of gold nanoparticles (AuNPs). Each NAEB gives highly enhanced Raman signals owing to the presence of well-defined plasmonic hot spots at junctions between AuNPs. Herein, the on-line SERS detection and accurate identification of suspended bacteria with a detection capability down to a single bacterium has been realized by the NAEB-DEP-Raman spectroscopy biosensing strategy. The practical detection limit with a measurement time of 10 min is estimated to be 70 CFU mL(-1) . In comparison with whole-cell enzyme-linked immunosorbent assay (ELISA), the SERS-nanoprobe-based biosensing method provides advantages of higher sensitivity and requiring lower amount of antibody in the assay (100-fold less). The total assay time including sample pretreatment is less than 2 h. Hence, this sensing strategy is promising for faster and effective on-line multiplex detection of single pathogenic bacterium by using different bioconjugated SERS nanoprobes.

A mechanistic analysis of the tetrasilyl-substituted trimetallaallenes, >E=E=E< (E = C, Si, Ge, Sn, and Pb).

The potential energy surfaces for the chemical reactions of tetrasilyl-substituted trimetallaallenes containing two cumulative E-E double bonds, where E = C, Si, Ge, Sn, and Pb, are studied using density functional theory (B3LYP/LANL2DZ). Two types of chemical reactions, methanol addition and intramolecular 1,2-silyl migration, are used to study the reactivity of these allene analogues. The theoretical investigations suggest that the relative reactivity increases in the order: >C-C-C< << >Si-Si-Si< < >Ge-Ge-Ge< < >Sn-Sn-Sn< < >Pb-Pb-Pb<. That is, the heavier the atomic weight of the group 14 atom (E), the more reactive is the >E-E-E< towards chemical reactions. Electronic (due to the group 14 element E) and steric (due to four bulky t-Bu2MeSi groups) factors play a key role in determining both the geometrical structures and the reactivity of the tetrasilyl-substituted trimetallaallenes, from both kinetic and thermodynamic viewpoints. A configuration mixing model, based on the work of Pross and Shaik, is used to rationalize the computational results. The results obtained allow a number of predictions, such as the reactivities and the reaction mechanisms of heavy allenes, to be made.