A multi-responsive sensor 1 was constructed by combining a ferrocene unit and a rhodamine block via a carbohydrazone bond. The sensor showed high selectivity toward Cu(2+) over other common metal ions in a wide pH range with excellent reversibility and rapid response. The obvious color change from colorless to pink upon the addition of Cu(2+) could make it a suitable 'naked-eye' indicator for Cu(2+). The detection limit (LOD) obtained was down to 2.0 nM and the association constant (Ka) was evaluated as 4.65 × 10(7) M(-1). The accuracy for detecting Cu(2+) in environmental river water was compared favorably with the traditional atomic absorption spectroscopy method (AAS). Finally, we proposed a reversible ring-opening mechanism (Off-On) of the rhodamine spirolactam induced by Cu(2+) binding and a 2 : 1 stoichiometric structure between 1 and Cu(2+).
An electrochemical sensing device with a plasticized polyvinyl chloride (PVC) membrane electrode based on a porphyrin derivative of p-amino tetraphenyl porphyrin (p-NH2TPP) for mercury ion (Hg2+) has been fabricated. The p-NH2TPP based PVC membrane electrode exhibited a nice linear potential performance for responding to Hg2+ in the range of 1.0×10-8 ~ 1.0×10-3 mol/L with a slope of 27.54 mV/-pC (25°C) in citrate buffer solution (pH=2.5). The detection limit was evaluated to be 7.5×10-9 mol/L. No obvious interferences were observed from Na+, K+, Ba2+, Mg2+, Ca2+, and Cr3+. The electrode possessed good stability and reproducibility. Comparing with atomic absorption spectroscopy (AAS), the electrode can be well applied to the determination of trace amount of Hg2+ in environmental waste water samples with a recovery rate of 94.83 ~ 104.78%. The sensing mechanism of the porphyrin derivative carrier for recognition of Hg2+has also been expounded by the formation of nice complexation effect between the lone pair electrons provided by four nitrogen atoms of the porphyrin molecule and unoccupied orbitals provided by the mercury ion.
An electronic detection method for DNA molecules based on an extended gate field effect transistor (EGFET) sensing chip has been presented in this paper, which consists of one gold plate electrode for molecule recognition and FET part for signal transduction. The DNA probe was prepared by first immobilization of a thiolated single-stranded oligonucleotide (T1) and then an alkanethiol such as 6-hydroxy-1-hexanethiol (6-HHT) on the gold plate. A fast cyclic voltammetry (FCV) was applied to quantification of DNA molecules by using a cathodic peak around -1.3 V at a electrode reaction, corresponding to reductive desorption in strong alkali solution. By using a 70.7 mV DC voltage onto a Ag/AgCl reference electrode, the electronic signals of EGFET were applied to detection of DNA molecules and its hybridization, and the corresponding hybridization efficient was estimated to be about 37.5%. About 1 ~ 4 DNA molecules per 100 nm2 on the Au substrate of EGFET could be counted, showing a promising sensing technique for bio-molecule.
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