Suyi Zhang

Colorimetric artificial tongue for protein identification

Artificial tongue systems are multisensory devices which are highly desirable for the analysis and recognition of complicated composition samples. Herein, a low-cost and simple colorimetric sensor array for identification and quantification of proteins were reported. Using prophyrin, porphyrin derivatives (mainly metalloporphyrins) and chemically responsive dyes as the sensing elements, the developed sensor array of artificial tongue showed a unique pattern of colorific change upon its exposure to proteins. The composite pattern for each sample was subjected to principal component analysis (PCA), thus providing a clustering map for more practical visualization. All the pure and mixed proteins, as well as denatured proteins, gave distinct patterns, thus resulting in their unambiguous identification. The PCA analysis also suggested that the unique pattern of colorific change may be due to the change of protein conformation and local environmental pH. These results demonstrate that the developed colorimetric artificial tongue system is an excellent sensing platform for identification and quantitative analysis of protein samples.

A Colorimetric Sensor Array for Identification of Natural Amino Acids

Abstract The development of colorimetric sensor array for the detection of natural amino acids is reported. Using a cross-responsive array containing a diverse family of chemically responsive dyes, the colorimetric sensor array provides enormous discriminatory power among different analytes. Digital imaging of the dye array before and after immersion provides a color change profile as a unique fingerprint for each specific analyte. The 6×6 array used in this research has 36 dyes that were sensitive to amino acids. A functional portable type apparatus was developed for data acquisition and data processing. Using colorimetric sensor arrays, 10 natural amino acids have been analyzed within 5 min of exposure at concentrations of 375 μM. The digital data library generated was analyzed with statistical and chemometric methods, including principal component analysis (PCA) and linear discriminant analysis (LDA). Facile identification of all the amino acids was readily achieved using comparison of the color change profiles or a PCA score plot. Using LDA analysis, the classification accuracy of identification was 97%. These results suggest that colorimetric sensor arrays may prove to be useful for the identification of natural amino acids, and they also represent a potential application in the field of cell recognition, food quality assurance, and microbial identification.

An Improved and Validated Sample Cleanup Method for Analysis of Ethyl Carbamate in Chinese Liquor

Ethyl carbamate (EC) is a potential human carcinogen widely existing in fermented foods and alcoholic beverages. The solid-phase extraction (SPE) coupled to gas chromatography mass spectrometry is a widely-used method to determine EC levels, but the accuracy varies with sample matrix and the effects of operation parameters are rarely examined. In this study, the influence factors involved in EC determination were investigated using Chinese liquor as sample matrix, and the improved method was further applied. Three types of SPE columns, including diatomite, Florisil, and primary-secondary amine, were compared in extraction efficiency, and the diatomite column exhibited the highest extraction efficiency. The optimal volumes of elution solvents with diatomite column were 15 mL for 3-mL samples solution loaded. In addition, the alcoholic strength for EC determination should be diluted below 20% (v/v) to avoid the enhancement of matrix-induced chromatographic response. Moreover, the pH neutralization could help improve EC recovery and peak resolution, reducing interfering effects. Based on these results, the improved method showed that the limit of detection, the limit of quantification, and average recoveries were 1.10 μg/L, 3.65 μg/L, and 93.06%, respectively. To further elucidate the underlying factors related to EC accumulation, partial least square regression analysis was conducted, and the results suggested that EC levels had the closest relationship with alcoholic strength among the remaining precursors.

Monitoring the adulteration of milk with melamine: a visualised sensor array approach

Melamine, a toxic triazine, is illegally used as an additive in milk to apparently increase the amount of protein, causing acute renal failure in thousands of Chinese infants. In this study, a rapid, simple, sensitive and selective colourimetric sensor array is reported as a potential screening tool for monitoring the adulteration of raw milk with melamine. Using chemically responsive dyes (mainly porphyrins and pH indicators) as the recognition elements, determination of melamine at different concentrations (0.1, 0.5, 1.0, 1.5 and 2.0 mg kg−1) and a detection limit of 0.1 mg kg−1 were achieved because of diverse and strong molecular interactions. Furthermore, the colourimetric sensor array was successfully able to discriminate between melamine and its analogues. The unique “fingerprint” of melamine was obtained with a novel signal processing method named “two-step subtraction”, which made it possible for the detection results to be easily observed with the naked eye even without any statistical analysis. In addition, the process including sample pre-treatment and detection process took only 12 min at room temperature. The merits (such as simplicity, rapidity, low cost, visual colourimetry, sensitivity and selectivity) make the proposed method especially useful for on-site screening of melamine levels in milk.

Role of Tryptophan in the Active Site of Plant Esterase: Chemical Modification and Fluorometric Studies

Plant esterase extracted from wheat flour play key roles in the spectrophotometric detection of organophosphorus compounds (OPs) for food safety and human health. The purpose of the present study was to investigate the role of tryptophan residues in the activity and structure of plant esterase by chemical modification and fluorometric studies. Active site characterization of purified plant esterase showed the involvement of tryptophan in the catalytic activity. Only one was essential for the enzyme activity by the Tsou’s analysis. Substrate protection experiments further confirmed that the tryptophan residue was located at the substrate-binding site. Fluorescence quenching studies elucidated that the tryptophan residues were largely exposed to the solvent, and a smaller fraction of the surface tryptophan residues had electropositively charged amino acids around them. Experimental results obtained here are expected to promote the applications of plant esterase in OPs detection. Further confirmation of the existence of other critical residues and detailed explanation of their functions were also required for the elucidation of the mechanism involved in the detection of OPs.

Molecular interactions of dimethyl methylphosphonate (DMMP) with metalloporphyrins: determination of the binding mechanism by spectroscopic methods.

The molecular interactions of 5,10,15,20-tetraphenylporphine zinc (ZnTPP) and 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (CoTPP) with dimethyl methylphosphonate (DMMP) have been investigated by absorption/absorption difference spectroscopy. The interactions between the metalloporphyrins and DMMP change the absorbance characteristics of the porphyrins resulted from the formation of the metalloporphyrin-DMMP complexes. According to the Benesi-Hildebrand (B-H) equation, the equilibrium constants and stoichiometries of the binding systems at four different temperatures (288, 293, 298 and 303 K) were obtained. Experimental results showed that both ZnTPP and CoTPP bind to DMMP via axial coordination, resulting in the formation of 1:1 metalloporphyrin-DMMP complexes. However, it was found that ZnTPP showed stronger binding capacity with the equilibrium constant (K) of 83.864 M(-1) at room temperature, while CoTPP exhibited weaker binding with K of 24.904 M(-1). The thermodynamic parameters, enthalpy change (Δ(r)H(m)(θ)), entropy change (Δ(r)S(m)(θ)) and free energy changes (Δ(r)G(m)(θ)) were also studied for the interactions, indicating that the formation of the metalloporphyrins-DMMP complex was an exothermic reaction.

Mechanism and kinetics of degrading aflatoxin B 1 by salt tolerant Candida versatilis CGMCC 3790

Four products were identified by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) for the degradation of aflatoxin B1 (AFB1) is by salt tolerant Candida versatilis CGMCC 3790 (C. versatilis CGMCC 3790), includingⅡ(C14H10O4), Ⅲ (C14H12O3), Ⅳ (C13H12O2), Ⅴ (C11H10O4), which were not toxic. Based on these products, it is speculated that AFB1 degradation has two pathways. The degradation ratio of active cell component (69.40%) and intracellular component (64.99%) was significantly higher than extracellular component (29.61%), suggesting that the AFB1 removal mainly resulted from biodegradation. The optimal degradation conditions of AFB1 (20 ng/mL) were: incubated at pH 5.0, 25 °C for 60 min in liquid medium system. The degradation ratio was ranged from 41.23%∼100% at 10.26∼130.44 ng/g in an actual system. This is the first report revealing that a salt tolerant yeast could effectively degrade AFB1. Therefore, Candida versatilis CGMCC 3790 might be an excellent candidate for bioremediation and detoxification for oriental fermentation condiment process.

Aflatoxin B1 degradation by salt tolerant Tetragenococcus halophilus CGMCC 3792

This study explores aflatoxin B1 (AFB1) degradation by salt tolerant Tetragenococcus halophilus CGMCC 3792 (T. halophilus CGMCC 3792). Six non-toxic degradation products of AFB1 were identified by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS), including m/z 243.06 (C14H10O4), 361.09 (C18H16O8), 229.09 (C14H12O3), 277.14 (C16H20O4), 217.12 (C14H16O2), 221.15 (C14H20O2). Two pathways were proposed based on molecular formulas and MS/MS spectra, and the final degradation product was m/z 221.15 (C14H20O2). The degradation ratio of active cell component (66%) and intracellular component (57%) was significantly higher than extracellular component (14%). AFB1 degradation ratio of intracellular component, initially at around 60%, was decreased to 32% after proteinase K treatment, and to 7% after heating, to 9% after proteinase K plus SDS treatment, and to 16% after TFA treatment. It suggests that the AFB1 removal mainly resulted from enzyme biodegradation. The degradation ratio was 92% in AFB1 polluted soy sauce mash. The high degradation ratio of AFB1 by T. halophilus CGMCC 3792 indicates its great potential for application in oriental fermentation condiment process.

A redox route for the fluorescence detection of lead ions in sorghum, river water and tap water and a desk study of a paper-based probe

In this paper, we developed a label-free fluorescence assay employing BSA-Au NCs, S2O32−, and 2-ME for the highly selective and sensitive detection of Pb2+ in sorghum, river water and tap water. When the BSA-Au NCs reacted with S2O32− in solution, Au(S2O3)23− complexes were formed immediately on the surfaces of BSA-Au NCs. After adding Pb2+ and 2-ME, the BSA-Au NCs rapidly dissolved to form Au–S complexes. As a result, the fluorescence intensity decreased dramatically, allowing quantification of Pb2+ in the aqueous solution. This reaction is highly specific under optimal detection conditions. A good linear relationship between the fluorescence intensity and the concentrations of Pb2+ could be obtained in the range of 10 to 1000 nM (R2 = 0.9910), with a detection limit (LOD; S/N ratio = 3) down to 1.043 nM. Significantly, compared with other studies, we greatly shortened the reaction time by substantial improvements in materials. On the basis of the above-mentioned work, we successfully immobilized S2O32− modified BSA-Au NCs on wax-printed papers to achieve the purpose of simple and real-time field monitoring of Pb2+. We picked up R-values (the red value of the RGB color model) from captured flurescence images under UV light (365 nm) and acquired a linear correlation between R-values and Pb2+ concentrations. This linear correlation exhibits the great potential of this approach. The proposed probe also showed satisfactory selectivity as well as excellent reproducibility. Multiple real sample experiments showed the tremendous prospect of this method, as well.

A Fluorescent detection method for copper ions based on a direct redox route and desk study of wax-printed paper-based probes

Cu2+ plays an important role in various fundamental physiological processes in organisms. Although Cu2+ probes have been developed, little research has focused on using a direct redox route to quench fluorescence for Cu2+ detection. Herein, a simple, label-free, cost-effective, and sensitive fluorescence method has been developed for Cu2+ detection. In the absence of Cu2+ and presence of NH3+ and SCN−, H2O2 was employed as an oxidant to corrode BSA–Au NCs, resulting in the disappearance of fluorescence. In contrast, in the presence of Cu2+, red fluorescence was maintained because Cu(NH3)62+ can decompose H2O2. Under optimal conditions, good linear correlation between the fluorescent response and Cu2+ concentrations ranging from 5 to 1250 nM was obtained (R2 = 0.9938). Furthermore, this monitoring method has successfully been applied to real urine, tap water, and sorghum extract samples, demonstrating the potential for field applications. Based on this work, we successfully immobilized BSA–Au NCs on wax-printed paper to accomplish real-time field Cu2+ detection. Fluorescence images were captured under UV light (365 nm), and R-values (red value of RGB color model) were analyzed. The obtained linear relationship between the R-value and the Cu2+ concentration demonstrated the potential of this approach. The developed probe also showed satisfactory selectivity and excellent reproducibility. Although previous methods required a masking agent to protect against interference from increasing Hg2+ concentration, Hg2+ and other interfering ions had a near-negligible effect on results in the present work.