This article reports on the synthesis of water dispersible carbon quantum dots (CDs) by a one-step hydrothermal method using polyamidoamine (PAMAM) and (3-aminopropyl)triethoxysilane (APTES) as a platform and passivant. The resulting CDs are highly uniform and finely dispersed. The synergistic effect between PAMAM and APTES on the surface of the CDs results in a fluorescence that is much brighter than that of CDs modified with either APTES or PAMAM only. The fluorescence of the co-modified CDs is quenched by Hg(II) ions at fairly low concentrations. Under the optimum conditions, the intensity of quenched fluorescence drops with Hg(II) concentration in the range from 0.2 nM to 10 μM, and the detection limit is 87 fM. The effect of potentially interfering cations on the fluorescence revealed a high selectivity for Hg2+. The fluorescent probe was applied to the determination of Hg(II) in (spiked) waters and milk and gave recoveries between 95.6 and 107 %, with relative standard deviation between 4.4 and 6.0 %.

In this work, we reported the synthesis of water-soluble carbon dots (CDs) by a one-step hydrothermal synthetic route using polyamidoamine (PAMAM) as platform and passivant, where the formation of CDs capped with PAMAM and the surface passivation were realized simultaneously. As a result, the prepared PAMAM-CDs were uniform, monodispersed sphere particles with an approximate diameter of about 2 nm, and the fluorescence and electrochemiluminescence (ECL) response of the nanocomposite film were enhanced. By combining the high sensitivity of ECL and the selectivity of immunoreactions, an ECL immunosensor for facile, rapid, and ultrasensitive detecting of ketamine was constructed, and the further application of the immunoassay was investigated. Under optimal experimental conditions, the obtained immunosensor showed a wide linear detection range from 0.2 to 200 ng mL−1 with a detection limit at 0.067 ng mL−1 in 0.1 M phosphate buffer solutions (pH 7.4). The immunosensor was successfully applied to the determination of ketamine in blood plasma. This kind of assay is expected to pave new avenues in label-free drug assays.

We report on a novel electrochemiluminescent (ECL) immunoassay for the ultrasensitive determination of morphine by making use of a gold electrode which was modified with a nanocomposite film containing self-assembled polyamidoamine (PAMAM) CdS quantum dots and electrodeposited gold nanoparticles (Au-NPs). The highly uniform and well-dispersed quantum dots were capped with PAMAM dendrimers. Due to the synergistic effect of the modified quantum dots and the electrodeposited Au-NPs, the ECL response is dramatically enhanced. Under optimal experimental conditions, the immunoreaction between morphine and anti-morphine antibody resulted in a decrease of the ECL signal because of steric hindrance. The calibration plot is linear in the morphine concentration range from 0.2 to 180 ng•mL−1, with a detection limit as low as 67 pg•mL−1. The sensor was successfully applied to the determination of morphine in blood plasma. This kind of assay is expected to pave new avenues in label-free drug assays.

In this study, a novel strategy for the construction of CdS quantum dots (QDs)-based electrochemiluminescence (ECL) sensor was developed. The stable nanocomposite film was obtained by using self-assembly CdS QDs capped with polyamidoamine (short for CdS-PAMAM) incorporating electrodeposited gold nanoparticles onto the surface of Au electrode. The water soluble CdS-PAMAM QDs were successfully synthesized by using PAMAM as a template and stabilizer. Based on the numerous reactive groups on the dendrimers, the high uniform and well-dispersed CdS-PAMAM QDs were assembled onto the surface of electrodeposited gold nanoparticles film. The feasibility of this manner was confirmed by photoluminescence, absorption spectra, scanning electron microscopy and electrochemical measurements. In addition, the ECL performance of the constructed CdS-PAMAM/GNPs film was investigated. With the synergistic effect of the CdS-PAMAM QDs and electrodeposited gold nanoparticles, the ECL response was dramatically enhanced. The fabricated nanocomposite film demonstrated rather high stability and sensitivity to dopamine detection. Under optimal experimental conditions, the fabricated sensor responded linearly to dopamine concentration in the range of 0.05–10 μmol L−1 with a detection limit of 0.012 μmol L−1. Moreover, the sensor exhibited good specificity, stability and reproducibility. The present work shows promising potential for developing new efficient ECL sensor.

Gold nanoparticles were prepared via a simple photoreduction technique in the presence of transition metal monosubstituted Keggin heteropolyanions (PW11M, M= Cu2+, Ni2+, Zn2+, Fe3+), in which PW11M acted as reducing agent, photocatalyst and stabilizer. The results indicated that the formation rate and morphology of the nanoparticles strongly depended on the kind of transition metal substituted in heteropolyacid and the preparation conditions, such as irradiation time and propan-2-ol amount. The photoreduction rates of PW11Zn and PW11Fe were faster than those of PW11Ni and PW11Cu. The shapes of the nanoparticles synthesized in the presence of PW11Fe and PW11Zn were nearly uniform spheres, whereas the morphologies of the nanoparticles synthesized in the presence of PW11Ni and PW11Cu were found to contain a mixture of flat triangular/hexagonal structures as well as spheres. Increases in the irradiation time and the propan-2-ol amount could make the morphology of nanoparticles uniform and shorten the formation time of the nanoparticles.

A novel reagentless immunosensor was fabricated by immobilization of redox mediator 3,3′,5,5′-tetramethylbenzidine (TMB) on the Nafion (Nf) film modified glassy carbon electrode. Gold nanoparticles were assembled onto the TMB/Nafion film modified electrode to provide active sites for the immobilization of antibody molecules. The antibody (anti-MIgG), in the present study, was fixed on the electrode for the rapid detection of antigen molecules (MIgG as a model analyte). The results showed that the immunosensor based on the immobilized TMB redox mediator exhibited good electrochemical response. A good linear relationship between peak current and the concentration of the MIgG was obtained in the concentration range from 4 to 120 ng/mL. The detection limit was estimated to be 1 ng/ml. Under the optimized conditions, the immunosensor exhibits good sensitivity, reproducibility and stability.

A novel charge-transfer compound (TMB)3PMo12O40 (TMB-PMo12, TMB = 3,3′,5,5′-tetramethylbenzidine) was synthesized. There is a strong electronic interaction between organic donor TMB and PMo12O403- heteropoly anion. Irradiation of ultraviolet light can cause the intramolecular electron-transfer between TMB and heteropoly anion in the complex. Electrochemical behavior of the TMB-PMo12 modified electrode in H2SO4 solution showed well-defined redox couples corresponding to the redox reactions of the incorporated TMB and heteropoly anion. The TMB-PMo12 modified electrode exhibits excellent catalytic activity for the reduction of IO3-, where the incorporated TMB may play an important role to activate the catalytic activity of the heteropoly anion.