Raman-based detection of bacteria using silver nanoparticles conjugated with antibodies

Surface enhanced Raman scattering (SERS) has been used to detect bacteria captured by polyclonal antibodies sorbed onto protein-A-modified silver nanoparticles. The selectivity and discrimination of the technique were assured by using a specific antibody to the model bacterium, Escherichia coli. As the SERS enhancement mechanism depends upon the metal surface proximity, 8 nm was considered as the optimum distance between the bacterium and the nanoparticle surface. Spectral reproducibility was verified using Principal Components Analysis to differentiate the clusters corresponding to the biomolecules and/or bacteria sorbed onto nanoparticles. Compared to the normal Raman spectrum, the SERS technique resulted in an intensity enhancement of over 20-fold.     

Fluorescence properties of gold nanorods and their application for DNA biosensing

This communication reveals new and unique optical properties with respect to enhanced fluorescence of gold nanorods as they elongate; a novel strategy for DNA hybridization studies based on monitoring the fluorescence intensity of gold nanorods has been demonstrated.     

Oxidation, deformation, and destruction of carbon nanotubes in aqueous ceric sulfate

A simple wet chemical method involving only ultrasonic processing in dilute ceric sulfate (CS) was used to functionalize carbon nanotubes (CNTs). Unexpectedly, single-walled and multiwalled carbon nanotubes (SWCNTs and MWCNTs) were cut, oxidized, and disintegrated by sonication in 0.1 N CS for 2-5 h. Transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), Raman scattering, and photoacoustic Fourier transform infrared spectroscopy (FTIR) were used to probe wall damage during the chemical processing. Cyclic voltammetry and impedance spectroscopy were used to evaluate the conductivity of the CS-treated CNTs. This one-step process resulted in the destruction of SWCNTs to produce nonconducting amorphous carbon. MWCNTs were oxidized and converted to graphitic materials and amorphous carbon with retained conductivity.     

Analysis of the 16 Environmental Protection Agency priority polycyclic aromatic hydrocarbons by high performance liquid chromatography-oxidized diamond film electrodes

The capabilities of using boron-doped diamond (BDD) thin films as electrode materials for analysis of the 16 US Environmental Protection Agency (EPA) priority polyaromatic hydrocarbons (PAHs) after a liquid chromatographic separation were evaluated. The BDD electrode was able to detect all 16 PAHs with high sensitivity due to the low background current and wide potential window. The method provided detection limits ranging from 12-40 nM (3-10 ppb) and repeatable results over consecutive analysis. Calibration curves were linear up to at least 10 microM for all PAHs. The work shows the promising use of diamond as an amperometric detector in high performance liquid chromatography (HPLC), especially for PAHs and other hydrophobic aromatic compounds.     

Electrochemically-assisted deposition of oxidases on platinum nanoparticle/multi-walled carbon nanotube-modified electrodes

Platinum nanoparticles were electrodeposited by a multi-potential step technique onto a multi-walled carbon nanotube (MWCNT) film pre-casted on a glassy carbon (GC) or boron-doped diamond (BDD) electrode. The MWCNT network consisted of Pt nanoparticles with an average diameter of 120 nm after an optimization of 36 deposition cycles. The resulting electrochemical sensors were capable of detecting hydrogen peroxide as low as 25 nM. Five different enzymes: glucose, lactate, glutamate, amino acid and xanthine oxidases, respectively, were deposited by a constant current technique for 5-10 min to form a stable and active biolayer for the analysis of their corresponding analytes. The glucose oxidase-based biosensor was linear up to 10 mM glucose with a detection limit of 250 nM and a response time of 5 s. Similar response times and detection limits were observed with glutamate, lactate, and amino acid oxidase despite the fact that the linear ranges were noticeably narrower. The mechanism of deposition was attributed to the decrease of local pH, created by oxygen evolution and effected enzyme precipitation.     

Detection of bacteria aided by immuno‐nanoparticles

Magnetic immuno‐nanorice particles were used for the capture and detection of Escherichia coli (E. coli) bacteria. The selectivity of the method was attained by attaching a specific anti‐E. coli antibody on the surface of the nanorice, binding exclusively to E. coli. The antibody attachment to the nanorice (60% sorption efficiency) took place through protein‐A molecules (82% uptake). Once E. coli was captured, the immuno‐nanorice‐bacteria complex was separated from the solution using the magnetic property of the nanorice. The detection of bacteria sorbed onto the immuno‐nanorice was accomplished using the ultra‐violet resonance Raman (UVRR) method, detecting single bacterial cells. Specific information concerning the aromatic residues tyrosine (Tyr), phenylalanine (Phe) and tryptophan (Trp) was derived. The discriminant function and cluster hierarchical analysis confirmed the specific and reliable bacteria‐detection capabilities. Copyright © 2007 John Wiley & Sons, Ltd.