Surface-enhanced Raman scattering using silver nanocluster on anodic aluminum oxide template sensor toward protein detection.

The affordable surface-enhanced Raman scattering (SERS) substrates, with a structure consisting of densely distributed round-shape silver nanoclusters on anodic aluminum oxide (AAO) template, is fabricated by magnetron sputtering and anodization processes. The physical investigations show that the silver nanoclusters with size distribution ranging from 10 to 30 nm uniformly distributed on the top and in the bottom of the AAO nanochannels. The SERS activities from adsorbed probe molecules, i.e., methylene blue, on the SERS substrate surface indicate a high Raman enhancement factor for trace organic analysis. The SERS substrate is successfully utilized in the detection of a trace amount of three different proteins, bovin serum albumin, immunoglobulin G, and cardiac troponin T, also adsorbed on the substrate surface. Several spectral bands containing important molecular structures of these proteins are clearly observed and identified. The obtained results indicated a step forward to label-free biomolecular detections in chip-based biosensors.

Cardiac troponin T detection using polymers coated quartz crystal microbalance as a cost-effective immunosensor.

Cardiac troponin T (cTnT) detection has been the focus of increased interest due to its role in myocardial infarction diagnosis. In this study, we report a relatively low coat technique to detect cTnT using a quartz crystal microbalance (QCM) sensor. A sensitive detection is achieved by introducing a QCM surface with a carboxylic polyvinyl chloride immobilization layer. The surface morphologies of this polymer film under varied deposition thickness have been investigated by field emission scanning electron microscopy and atomic force microscopy. A cTnT detection result from a modified QCM surface can be obtained within a short response time by a direct detection of the immunoreaction and a direct conversion of mass accumulation into a frequency shift, representing a measurable electrical signal. The relationship between the cTnT concentration and the response current from a QCM sensor shows detectability at the concentration of cTnT as low as 5 ng/ml.

High sensitivity electrochemical cholesterol sensor utilizing a vertically aligned carbon nanotube electrode with electropolymerized enzyme immobilization.

In this report, a new cholesterol sensor is developed based on a vertically aligned CNT electrode with two-step electrochemical polymerized enzyme immobilization. Vertically aligned CNTs are selectively grown on a 1 mm(2) window of gold coated SiO(2)/Si substrate by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. CNTs are then simultaneously functionalized and enzyme immobilized by electrochemical polymerization of polyaniline and cholesterol enzymes. Subsequently, ineffective enzymes are removed and new enzymes are electrochemically recharged. Scanning electron microscopic characterization indicates polymer-enzyme nanoparticle coating on CNT surface. Cyclic voltammogram (CV) measurements in cholesterol solution show the oxidation and reduction peaks centered around 450 and -220 mV, respectively. An approximately linear relationship between the cholesterol concentration and the response current could be observed in the concentration range of 50-300 mg/dl with a sensitivity of approximately 0.22 µA/mg·dl(-1), which is considerably higher compared to previously reported CNT bioprobe. In addition, good specificity toward glucose, uric acid acetaminophen and ascorbic acid have been obtained. Moreover, sensors have satisfactory stability, repeatability and life time. Therefore, the electropolymerized CNT bioprobe is promising for cholesterol detection in normal cholesterol concentration in human blood.