Guomei Zhang

Biosensors for determination of glucose with glucose oxidase immobilized on an eggshell membrane

A glucose biosensor using an enzyme-immobilized eggshell membrane and oxygen electrode for glucose determination has been fabricated. Glucose oxidase was covalently immobilized on an eggshell membrane with glutaraldehyde as a cross-linking agent. The glucose biosensor was fabricated by positioning the enzyme-immobilized eggshell membrane on the surface of a dissolved oxygen sensor. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution and the decrease in the oxygen level was monitored and related to the glucose concentration. The effect of glutaraldehyde concentration, pH, phosphate buffer concentration and temperature on the response of the glucose biosensor has been studied in detail. Common matrix interferents such as ethanol, d-fructose, citric acid, sodium benzoate, sucrose and l-ascorbic acid did not give significant interference. The resulting sensor exhibited a fast response (100s), high sensitivity (8.3409mgL(-1) oxygen depletion/mmolL(-1) glucose) and good storage stability (85.2% of its initial sensitivity after 4 months). The linear response is 1.0x10(-5) to 1.3x10(-3)molL(-1) glucose. The glucose content in real samples such as commercial glucose injection preparations and wines was determined, and the results were comparable to the values obtained from a commercial glucose assay kit based on a spectrophotometric method.

Study on the interaction of methylene blue with cyclodextrin derivatives by absorption and fluorescence spectroscopy.

The ability of beta-cyclodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), and carboxymethyl-beta-cyclodextrin (CM-beta-CD) to break the aggregate of the methylene blue (MB) and to form 1:1 inclusion complexes has been studied by absorption and fluorescence spectroscopy. Experimental conditions including concentrations of various cyclodextrins (beta-CD, HP-beta-CD and CM-beta-CD) and media acidity were investigated for the inclusion formation in detail. The formation constants are calculated by using steady-state fluorimetry, from which the inclusion capacity of different cyclodextrins (CDs) is compared. The results suggest that the charged beta-cyclodextrin (CM-beta-CD) is more suitable for inclusion of the cationic dye MB than the neutral beta-cyclodextrins (beta-CD, HP-beta-CD) at pH>5. A mechanism is proposed which is consistent with the stronger binding of MB with CM-beta-CD compared with the other CDs at pH>5.

Investigation on the inclusion behavior of neutral red with β-cyclodextrin, hydroxypropyl-β-cyclodextrin and sulfobutylether-β-cyclodextrin

Abstract The formation of the inclusion complexes of neutral red (NR) with cyclodextrins (CDs) including β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and sulfobutylether-β-cyclodextrin (SBE-β-CD) was studied by fluorescence and UV-Vis absorption spectroscopy and the binding constants ( K ) of the inclusion complexes were obtained by steady-state fluorescence measurements. Experimental conditions including the concentrations of various CDs and media acidity were investigated in detail. The results suggested that NR exists in two molecular forms in aqueous solution (the acidic form and the neutral form). CDs were most suitable for inclusion of the neutral form of NR and could cause enhanced fluorescence emission and absorption by NR. Moreover, the effect of the charged CD (SBE-β-CD) was quite different from that of the uncharged CDs (β-CD and HP-β-CD). A mechanism is proposed to explain the inclusion process.

Controllable synthesis of green and blue fluorescent carbon nanodots for pH and Cu(2+) sensing in living cells.

We report a controllable strategy for fabrication of green and blue fluorescent carbon nanodots (CDs), and demonstrate their applications for pH and Cu(2+) sensing in living cells. Green and blue fluorescent CDs have been synthesized by hydrothermal method and pyrolysis of leeks, respectively, providing an easy way for the production of CDs without the request of tedious synthetic methodology or the use of toxic/expensive solvents and starting materials. Green fluorescent CDs (G-CDs) exhibit high tolerance to pH values and external cations. Blue fluorescent CDs (B-CDs) can be applied to pH and Cu(2+) sensing. The linear range of Cu(2+) detection is 0.01-10.00 μM and the detection limit is 0.05 μM. For pH detection, there is a good linearity in the pH range of 3.5-10.0. The linear and rapid response of B-CDs to Cu(2+) and pH is valuable for Cu(2+) and pH sensing in living cells. Confocal fluorescent imaging of human cervical carcinoma cells indicates that B-CDs could visualize Cu(2+) and pH fluctuations in living cells with negligible autofluorescence.

A reversible fluorescent pH-sensing system based on the one-pot synthesis of natural silk fibroin-capped copper nanoclusters

A one-pot “green” synthesis of water soluble and pH-responsive natural silk fibroin (SF)-stabilized fluorescent copper nanoclusters (CuNCs) was reported without using any additional reducing agents, and the as-prepared SF@CuNCs exhibited a fluorescence emission at 420 nm with highly stable properties. The reversible pH sensor of the fluorescent SF@CuNCs has been designed based on the obvious fluorescence enhancing properties of CuNCs. Significantly, the SF@CuNCs described here were employed as pH sensors by virtue of the fluorescence intensity of their sensitive response to fluctuating pH in a linear range of 6.08–10.05. Meanwhile, the fluorescence intensity of the SF@CuNCs increased by around 8-fold at high pH values compared with a low pH of 6.08. As expected, the pH sensor was sensitive to different buffer solutions, and also presented a good linear relationship in different buffer solutions. Besides, the ionic strength of the buffers had a slight influence on the pH-responsive behavior and various metal ions showed almost no effects. The proposed method was successfully used to detect the pH of real water samples, thereby indicating its potential practical application.

Gold nanoclusters as fluorescent sensors for selective and sensitive hydrogen sulfide detection

As a highly toxic environmental pollutant and also an important gasotransmitter in diverse physiological processes, the selective and sensitive detection of hydrogen sulfide (H2S) is very significant. In this work, acetylcysteine stabilized gold nanoclusters (ACC@AuNCs)-based fluorescent sensors had been successfully constructed for H2S perception. The sensing principle was that H2S-induced fluorescence quenching of AuNCs which attributed to both the formation of Au2S between Au(I) in the AuNCs and H2S and the increased particle size. The proposed sensors showed high selectivity toward H2S over other anions, amino acids and thiols, and exhibited a stable response for H2S from 0.002 to 120μmolL-1 with a detection limit of 1.8nmolL-1. In addition, the practical application of the designed sensors was further evaluated with water and serum samples, and the tested results agreed well with those obtained by ICP-AES method. The satisfactory recoveries and good precision show that the proposed fluorescent sensors has potential application in biological and environmental fields.

Facile one-pot synthesis of Au(0)@Au(I)–NAC core–shell nanoclusters with orange-yellow luminescence for cancer cell imaging

We report a facile strategy to synthesize ultrabright core–shell gold nanoclusters in one pot by using N-acetyl-L-cysteine (NAC) as both a reducing and protecting agent, in which the core is Au(0) atoms and the shell is oligomeric Au(I)–NAC complexes. The Au(0)@Au(I)–NAC core–shell nanoclusters (NCs) displayed excitation and emission bands at 340 and 590 nm, respectively. It showed a strong orange-yellow photoluminescence with a quantum yield of 14%. The thermogravimetric analysis and mass spectrometry data suggest that the as-synthesized NCs comprise mainly Au27NAC32, in which a uniquely high thiolate-to-Au ratio (1.2 : 1) endows the gold clusters better biocompatibility. The Au(0)@Au(I)–NAC core–shell NCs offered ultra-small size, excellent stability, large Stokes shift and microsecond-scale lifetime, and exhibited negligible cytotoxicity to cancer cells. Based on the excellent properties of the gold nanoclusters (AuNCs), cell experiments were conducted. Cytotoxicity studies showed that the AuNCs exhibited negligible effects in altering cell proliferation or triggering apoptosis. The as-synthesized AuNCs have been successfully applied as a photoluminescent probe for human bladder cancer cellular imaging.

Study of the contact charge transfer behavior between cryptophanes (A and E) and fullerene by absorption, fluorescence and 1H NMR spectroscopy.

A group of novel cage-like compounds cryptophanes A and E were synthesized from vanillin by a three-step method. The intermolecular interaction between cryptophanes (A and E) and fullerene (C(60)) was investigated in detail by absorption, fluorescence and (1)H NMR spectroscopy. The absorption of C(60) at 410-650 nm decreased in the presence of cryptophanes A or E. The decrease in absorption intensity was proportional to the concentration of cryptophanes A or E. On the other hand, the fluorescence intensity of cryptophanes A or E decreased and the emission maxima were blue-shifted with the increase in C(60) concentration. These results suggest that contact charge transfer (CCT) complexes can be formed from C(60) with cryptophanes A or E. In addition, the electrochemical behavior of cryptophanes (A and E) and C(60) was studied by cyclic voltammetry. The redox currents of cryptophanes (A and E) decreased and the peak potentials were shifted on addition of C(60). The changes in the chemical shifts (Delta delta) of aromatic protons of cryptophanes (A and E) in their NMR spectra further support that CCT complexes were formed with cryptophanes as the electron donors and C(60) as the electron acceptor.

A highly selective ratiometric fluorescent probe for biothiol and imaging in live cells

A new N-butyl-4-amino-1,8-naphthalimide-based colorimetric and ratiometric fluorescent probe for the detection of biothiols (cysteine, homocysteine, and glutathione) was designed and synthesized. The probe exhibited good selectivity and sensitivity toward biothiols over other non-thiol-bearing amino acids and common anions with significant changes in both color (from colorless to yellow) and fluorescence (from blue to yellow-green). The mechanism is based on cleavage of disulfide by thiols followed by an intramolecular cyclization to give the product, N-butyl-4-amino-1,8-naphthalimide, which showed outstanding intramolecular charge transfer (ICT). Therefore, ratiometric fluorescence signal was observed. Furthermore, the probes were successfully applied for visualizing endogenous thiols in living cells.

Rapid one-pot synthesis of MMTA protected fluorescent gold nanoclusters for selective and sensitive detection of ferric ion

Herein, we demonstrate a straightforward synthesis of fluorescent gold nanoclusters (AuNCs), employing 2-Mercapto-4-methyl-5-thiazoleacetic acid (MMTA) as a reducing and protecting agent by a rapid one-pot synthesis method with a short time of 20min. The as-synthesized MMTA-AuNCs exhibited bright blue emission with a strong peak centered at 430nm and the quantum yield (QY) was evaluated to be 4.0%. Based on the fluorescence quenching mechanism of a surface chelating reaction between MMTA and ferric ion (Fe3+), the MMTA-AuNCs were exploited as a fluorescence sensor for sensitive and selective detection of Fe3+. Two linear ranges of 9.9-3000.0nM and 3.0-1100μM with a detection limit of 3.0nM were obtained. The detection limit was lower than the maximum level (0.3mgL-1, equivalent to 5.4μM) of Fe3+ permitted in drinking water by the U.S. Environmental Protection Agency. Furthermore, the proposed fluorescent sensing system was successfully applied to the analysis of Fe3+ in real samples such as water and human serum samples with satisfactory recoveries. These results indicated that the as-prepared MMTA-AuNCs could pave an avenue for the development of sensing probes for detection of Fe3+ in environmental and biomedical applications.