Sensitive detection of trace bisphenol A (BPA) in water samples has been accomplished via inhibition of luminol chemiluminescence (CL) by BPA on the silver nanoparticles (AgNPs)-enhanced luminol–KMnO4 CL system for the first time. Under the optimized experimental conditions, the CL intensity was found to be proportional to the concentration of BPA ranging from 1.0 × 10−8 to 5.0 × 10−5 g L−1. The detection limit (3σ) was estimated to be 1 × 10−9 g L−1. Such a concentration level is approximately 1–4 orders of magnitude lower than those reported by other methods. The feasibility of the method for determination of BPA in real water samples has been demonstrated. Via examining CL and UV–vis spectra of the CL system, possible mechanism inherent in the AgNPs-enhanced CL assay and the follow-up inhibition of BPA on the above system was proposed. The method described herein is simple, selective and obviates the need of extensive sample pretreatment.

A major constituent in the deposit of the brain in a patient with Alzheimer’s disease (AD) is the aggregates/fibrils of amyloid-β (Aβ) peptides containing 39−43 amino acids. The total Aβ levels and the concentration ratio between the most abundant Aβ(1−40) peptide and the more aggregation-prone Aβ(1−42) in body fluids (e.g., cerebrospinal fluid or CSF) have been suggested as possible criteria for early diagnosis of AD. By immobilizing capture antibodies specific to the two peptides in separate fluidic channels, surface plasmon resonance (SPR) has been used to quantify Aβ(1−40) and Aβ(1−42) present in CSF samples collected from AD patients and healthy donors. With signal amplification by streptavidin conjugated to an antibody that is selective to the common N-terminus of the Aβ peptides, concentrations as low as 20 pM can be readily measured. The range of Aβ peptide concentrations measurable by this method spans 4 orders of magnitude. The ability of regenerating the sensor surface for repeated measurements not only improves the reproducibility but also enhances the sample throughput. Our data reveal that the ratio of Aβ(1−40) concentration versus Aβ(1−42) concentration in CSF samples from AD patients is almost twice as high as that from healthy persons. In contrast to the commonly used enzyme-linked immunosorbent assay (ELISA), SPR obviates the need of a more expensive and less stable enzyme conjugate and the use of carcinogenic substrate for the signal detection and allows the binding events to be monitored in real time.

A novel fluorescent CdS-encapsulated DNA nanocomposite was synthesized via alternate adsorption of Cd2+ and S2− onto the DNA template affixed inside an agarose gel. Confining DNA molecules in the gel matrix reduces the flexibility of the DNA strand, which facilitates the formation of a uniform coating of CdS onto the DNA template. The resultant rod-shaped nanocomposite (40−90 nm in width and 200−300 nm in length) is well dispersed in solution and fluoresces at 330 nm upon excitation at either 228 or 280 nm. The fluorescence is attributed to tiny particles present in the CdS coating. It was found that the fluorescence can be significantly quenched by trace amount of Hg2+. The high selectivity toward Hg2+ and the apparent change in the CdS coating upon exposure to Hg2+ indicate that Hg2+ has reacted with the CdS coating through formation of the much more insoluble HgS and the bridging S−Hg−S bonds at the surface. The extent of quenching is dependent on the concentration of Hg2+ in the range of 0.04−13 μM, and a remarkable detection limit (8.6 nM at 30 °C and 4.3 nM at 50 °C) can be achieved. The feasibility of the method for the analysis of Hg2+ in a wastewater sample was demonstrated with an excellent relative standard deviation (RSD, 3.4%). The method described herein is simple, selective, and sensitive and obviates the need of extensive sample pretreatment or special instrumentation.

Simultaneous determination of wild-type and total p53 proteins (wild-type and mutant combined) present in cancer cell lysates has been performed with a dual-channel surface plasmon resonance (SPR) instrument. To achieve specificity, each channel of the SPR chip was modified with a consensus double-stranded (ds-) DNA and a monoclonal antibody. The high affinity of the consensus ds-DNA to the wild-type p53 and the antibody to total p53 results in remarkably low detection levels (10.6 and 1.06 pM for the wild-type and total p53, respectively). The difference between the SPR signals reveals the extent of p53 mutation, which is indicative of cancer development. The SPR signals increase with the p53 concentration across a wide range (from low picomolar to nanomolar levels) that amply encompasses the typical cellular p53 concentrations. The applicability of the method to real sample analysis has been demonstrated with the comparative analyses of normal and cancer cell lysates. The normal cell samples all displayed significantly higher levels of wild-type p53. In contrast, elevated levels of mutant p53 were observed from the cancer cell lysates. In comparison with enzyme-linked immunosorbant assay (ELISA), SPR obviates the need of a second antibody labeled with an enzyme in the “sandwich enzyme immunoassay” format and is capable of real-time monitoring of the binding events. Thus, SPR could potentially serve as an attractive technique for rapid, sensitive, reliable, and label-free cancer diagnoses.

The interaction of tumor suppressor p53 with apo-metallothionein (apo-MT) has been carried out using a flow injection-surface plasmon resonance (FI-SPR) instrument. MT was first tethered onto the carboxymethylated dextran film. Via incorporation of glycine–HCl (pH 2) to remove the sequestrated metal ions inherent in MT molecules, a more extended and open structure of apo-MT was formed. Substantial SPR angle shift corresponding to the interaction of wild-type p53 with apo-MT was observed. The interaction was originated from the binding between the free sulfhydryl groups of apo-MT and Zn2+ of p53 with the binding constant of 1.4 × 108 M−1. The specific binding of p53 to consensus double-stranded DNA was hindered after metal chelation from p53 by apo-MT. Furthermore, inhibition of the interaction between p53 and apo-MT imposed by p53/DNA complex was observed. The fluorescence measurements also revealed the binding of p53 to apo-MT, being consistent with the SPR results. Thus, SPR could potentially serve as an attractive technique for monitoring p53 conformational change and transcriptional activity regulated by the MT/apo-MT couple.