Efficient detection of aklomide/nitromide based on a sensor of MPA capped CdTe QDs using fluorescence quenching method.

Based on the fluorescence sensor of 3-Mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs), two novel detection methods for aklomide and nitromide were developed. The MPA-CdTe QDs were synthesized and characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), ultraviolet visible (UV-vis) and fluorescence (FL). The quenchings were all static. The binding constants (Ka) at different temperatures were obtained. Electrostatic forces were the main forces for the two bindings. For the detection of aklomide and nitromide, under the optimal conditions, the effects of some metal ions, glucose, bovine serum albumin (BSA) and congeneric drug on the determination were explored. The standard equations were established and the limits of detection (LOD) were 0.0215 and 0.0388 µg mL-1 (3S0/S), repectively. The methods were applied to analyse the samples of chicken and duck, the recoveries were 99.41 % - 101.24 % with RSDs of 0.29 % - 1.19 % (n = 5).

Sensitive detection of dextromethorphan hydrobromide based on portable Raman spectrometer and CuO@AgNPs nano composite SERS substrate.

A highly sensitive surface-enhanced Raman spectroscopy approach was established for the detection of dextromethorphan hydrobromide (DXM) utilizing nano CuO modified silver nanoparticles (CuO@AgNPs) as substrate. Ultraviolet visible spectra (UV-vis), X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterized the synthesized CuO@AgNPs. UV-vis and fourier transform infrared (FT-IR) were adopted to investigate the interaction between DXM and CuO@AgNPs. The optimal experimental conditions (the dosages of CuO@AgNPs and NaCl as well as mixing time) were explored. The enhancement factor (EF) was 1.71 × 106. The linear relationship between SERS intensity and the concentration of DXM in the range of 67 - 1000 nmol L-1 was obtained as ISERS = 25.81 c + 40398.77, and the limit of detection (LOD) was 2.12 nmol L-1 (S/N = 3). The interference of K+, Mg2+, Zn2+, Ca2+, Cu2+, Fe3+, glucose, HSA, L-tryptophan, soluble starch and ibuprofen were investigated. The method was successfully applied to test DXM in serum samples. The recovery was 99.06% - 101.51% with the relative standard deviation (RSD) of 0.74% - 3.87%.

A sensitive surface-enhanced Raman spectroscopy detection for gentamicin and tobramycin using γ-Al2O3-modified silver nanoparticles coated with bovine serum albumin as substrate.

Two aminoglycoside antibiotics (AGs), gentamicin (GEN) and tobramycin (TOB), have good antibacterial activity against most pseudomonas aeruginosa and staphylococcus. The molecular structure of these drugs lack chromogenic groups, which brings challenges to their detection. In this project, the detecting methods for GEN and TOB utilizing surface-enhanced Raman spectroscopy (SERS) based on γ-Al2O3-modified silver nanoparticles (AgNPs) coated with bovine serum albumin (BSA) were established. The enhancement factors (EFs) of GEN and TOB were 2.44 × 105 and 2.67 × 106, respectively. The transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and spectrophotometric techniques were used to characterize the substrate and the combination of the substance with drugs. The pH, the addition amounts for the substrate and coagulant, as well as the mixing time were optimized. On the basis of single factor experiments, a more scientific response surface model was established. The concentrations of GEN and TOB showed good linear relationships with their Raman signals in the ranges of 6.67 × 10-8 - 2.00 × 10-6 and 6.67 × 10-9 - 3.00 × 10-7 mol L-1 respectively. The limits of detection (LODs) were 11.88 and 1.26 nmol L-1 for GEN and TOB, respectively. The methods were used successfully for the samples determination of the two AGs in commercial drugs and meat products.

A fluorescence nanoprobe of N-Acetyl-L-Cysteine capped CdTe QDs for sensitive detection of nitrofurazone.

A method was established for detecting the content of nitrofurazone (NFZ) by fluorescence quenching of N-Acetyl-L-Cysteine (NAC) coated cadmium telluride quantum dots (CdTe QDs). By means of transmission electron microscopy (TEM) and multispectral methods such as fluorescence and ultraviolet visible spectra (UV-vis), the synthesized CdTe QDs were characterized. The quantum yield (φ) of CdTe QDs was measured as 0.33 by reference method. The CdTe QDs had a better stability, the RSD of fluorescence intensity was 1.51% in three months. NFZ quenching the emission light of CdTe QDs was observed. The analyses of Stern-Volmer and time-resolved fluorescence suggested the quenching was static. The binding constants (Ka) between NFZ and CdTe QDs were 1.14 × 104 (293 K), 0.74 × 104 (303 K) and 0.51 × 104 (313 K) L mol-1. The hydrogen bond or van der Waals force was the dominated binding force between NFZ and CdTe QDs. The interaction was further characterized by UV-vis absorption as well as Fourier transform infrared spectra (FT-IR). Using fluorescence quenching effect, a quantitative determination of NFZ was carried out. The optimal experimental conditions were studied and determined as following: pH was 7 and contact time was 10 min. The effects of reagent addition sequence, temperature and the foreign substances including some metals (Mg2+; Zn2+; Ca2+; K+; Cu2+), glucose, bovine serum albumin (BSA) and furazolidone on the determination were studied. There was a high correlation between the concentration of NFZ (0.40 - 39.63 µg mL-1) and F0/F with the standard curve F0/F = 0.0262c + 0.9910 (r = 0.9994). The detection limit (LOD) reached 0.04 µg mL-1 (3S0/S). The contents of NFZ in beef and bacteriostatic liquid were detected. The recovery of NFZ was 95.13% - 103.03% and RSD was 0.66% - 1.37% (n = 5).

Rapid determination of isepamicin by using SERS based on BSA-protected AgNPs modified by α-Fe2O3.

A surface-enhanced Raman spectroscopy (SERS) method for the determination of isepamicin (ISE) using silver nanoparticles (AgNPs) protected by bovine serum albumin (BSA) and modified by α-Fe2O3 as an efficient substrate was established. The synthesized substrate was characterized and verified by transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis), and fourier transform infrared spectroscopy (FT-IR). The conditions affecting the Raman signal of ISE were optimized by single factor and response surface experiments. Under optimized conditions, a standard curve ISERS = 43.08c + 63598.69 (c: nmol/L) with a linear relationship (r = 0.9976) was established between the SERS intensity and ISE concentration in the range of 20.00 - 2000.00 nmol/L. The limit of detection (LOD) for ISE was 16.58 nmol/L (S/N = 3). The recovery of ISE in the samples was 96.29 % - 104.12 %, with relative standard deviation (RSD) was 1.53 % - 3.43 % (n = 5). The SERS method was reliable and satisfactory for the quantitative analysis of ISE at low concentration.

Exploring the intercalation binding of tiamulin with DNA using multispectroscopy and a molecular modelling approach.

The binding of tiamulin with calf thymus DNA was systematically investigated using multispectroscopy and molecular modelling techniques. For DNA, once tiamulin was added, viscosity (η) and melting temperature (Tm ) both exhibited an uptrend. The fluorescence performance of the tiamulin-DNA complex did not change with the ionic strength changes. The binding constant (Ka ) of tiamulin for single-stranded DNA (ssDNA, 1.48 × 104 M-1 ) was obviously higher than that for double-stranded DNA (dsDNA, 9.51 × 103 M-1 ) at 291 K. The helix structure became looser and the base stack force became stronger for DNA due to the presence of tiamulin as seen from circular dichroic (CD) spectra. The intercalation binding mode of tiamulin with DNA was disclosed. Molecular modelling also revealed tiamulin inserting into the base pairs with the lowest binding free energy of -18.73 kJ mol-1 using van der Waals forces as well as hydrogen bonds.

Sensitive surface-enhanced Raman spectroscopy (SERS) determination of nitrofurazone by ß-cyclodextrin-protected AuNPs/γ-Al2O3 nanoparticles.

A novel surface-enhanced Raman spectroscopy (SERS) method for the determination of nitrofurazone was developed using AuNPs/γ-Al2O3 nanoparticles protected by ß-cyclodextrin (ß-CD) as substrate prepared in our lab. The optimum experimental conditions were obtained from single factor procedure and response surface modeling. A linear relationship (ISERS = 508.96c + 31987.87, c: nmol L-1, R2 = 0.996) between SERS intensity and the concentration of nitrofurazone in the range of 3.3 - 667.0 nmol L-1 was established, the limit of detection (LOD) was found at nmol L-1 level (0.37 nmol L-1 by 3S0/S). The selectivity for the method was studied by the influences of foreign substances on the determination. The recoveries and RSD (n = 5) for the six meat samples were 95.1 % - 104.5% and 2.4 % - 4.8% respectively, which suggesting that the new SERS method was successfully to detecting nitrofurazone.

Multispectral and molecular modeling investigations on the binding behaviors of two anticoccidials with serum albumins.

The interaction properties of monensin/clopidol with bovine/human serum albumin (BSA/HSA) were determined via multispectral together with molecular modeling techniques in the report. Fluorescence quenching spectra at different temperatures and fluorescence lifetime determination demonstrated that the fluorescence quenching belonged to a static quenching type. In the case of monensin-BSA, clopidol-BSA, monensin-HSA and clopidol-HSA, the binding constants Ka (291 K) were 5.42 × 104, 4.96 × 104, 3.22 × 104 and 2.99 × 104 M-1, respectively; the binding distances r0 were 1.88, 2.53, 2.19 and 2.02 nm, respectively. Monensin and clopidol bound strongly with BSA/HSA with binding free energies equal to -26.37/-25.11 and -26.11/-24.93 kJ mol-1, respectively. The spontaneous binding process was dominated by hydrogen bonds and van der Waals forces as reflected in thermodynamic parameters analyses. Synchronous, CD, FTIR and UV-vis spectra assays confirmed that serum albumins conformations were altered. Using competitive experiment, monensin/clopidol was observed to bind at site I of serum albumins, which were reconfirmed by the results of molecular modeling.Communicated by Ramaswamy H. Sarma.

Assessment on the binding characteristics of residual marbofloxacin in animal-derived food to bovine/human serum albumin by spectroscopy and molecular modelling.

To assess the toxicity of residual marbofloxacin from animal-derived food, the interaction characteristics of marbofloxacin to bovine/human serum albumins (BSA/HSA) were explored using spectroscopic methods combined with molecular modelling. According to fluorescence spectra and time-resolved fluorescence spectra measurements, quenching of BSA/HSA fluorescence induced by marbofloxacin was characterized as static quenching. A 1:1 ground-state complex of marbofloxacin to BSA/HSA was formed with binding constant (Ka ) 1.66 × 104 /9.74 × 103 M-1 at 291 K. The location of marbofloxacin binding at site I within BSA/HSA was clarified by site marker competitive experiments. Molecular modelling demonstrated that the binding region for marbofloxacin to BSA and HSA were at site I with the lowest binding free energies of -22.86 and -21.60 kJ mol-1 , respectively. Hydrogen bonds and van der Waals forces were dominantly involved in the spontaneous binding. Nonradiation energy transferred from BSA and HSA to marbofloxacin, due to the close distance (r0 ) between marbofloxacin and Trp residues of BSA (4.28 nm) and HSA (3.34 nm). As explained by circular dichroism (CD) spectra, an increased BSA/HSA α-helix structure was observed after binding to marbofloxacin. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectra suggested that conformation of the two proteins was altered by marbofloxacin.

Study on the binding of sulfaclozine sodium monohydrate with bovine and human serum albumins using multi-spectroscopy and molecular docking.

The interactions of sulfaclozine sodium monohydrate (SSM) with bovine and human serum albumins (BSA and HSA) were studied by multi-spectroscopy and molecular docking technique. Stern-Volmer analysis and fluorescence lifetime measurements suggested the quenching processes were static. According to the Fluorescence resonance energy transfer (FRET) theory, the binding distances were obtained indicating SSM interacted with BSA/HSA along with non-radiation energy conversion. Electrostatic attraction was the main force in keeping the stability of the compound based on thermodynamic parameters. Circular dichroism (CD), synchronous fluorescence and Fourier Transform infrared (FT-IR) spectra embodied the secondary structures of serum albumins were transformed by SSM. The site marker competitive and molecular docking measurements testified SSM bound to BSA/HSA at site I. In conclusion, the secondary structures of BSA/HSA were changed by SSM in the static fluorescence quenching processes with the non-radiation energy conversion. The binding sites were all located at site I and electrostatic attraction was the main force for the new compound. Communicated by Ramaswamy H. Sarma.

Rapid determination of marbofloxacin by surface-enhanced Raman spectroscopy of silver nanoparticles modified by ß-cyclodextrin.

A novel surface enhanced-Raman spectroscopy (SERS) assay for marbofloxacin was developed based on ß-cyclodextrin-modified silver nanoparticles (ß-CD-AgNPs). The marbofloxacin could interact with ß-CD-AgNPs and a new assembly was formed by AgN covalent bond. This assembly was characterized by the spectra of FT-IR and UV-vis. The optimal measurement conditions were studied in detail. In 0.033 mol L-1 HCl solution, marbofloxacin had a sensitive SERS signal at 806 cm-1. The enhancement factor (EF) was 2.11 × 107. There was a good linear correlation between the concentration of marbofloxacin and SERS intensity: the linear range was 0.003-0.03 µmol L-1 (r2 = 0.996). The limit of detection (LOD) (S/N = 3) was 1.7 nmol L-1 (S/N = 3). Moreover, the influence of some interferences including Cu2+, K+, Zn2+, Ca2+, Na+, Mg2+, glucose and tiamulin on the determination were studied. The developed SERS method was used to detect the content of marbofloxacin in chicken and duck, the recovery was 101.3%-103.1% with RSD 4.07%-6.83%.

Spectral and molecular docking studies on the interaction of three flavonoids with bovine serum albumin.

Communicated by Ramaswamy H. Sarma.

Multispectral and molecular docking investigations on the interaction of primethamine/trimethoprim with BSA/HSA.

Primethamine (PMA) and trimethoprim (TMP) were investigated as traditional coccidiostats on the binding of bovine serum albumin (BSA) and human serum albumin (HSA) by multispectral and molecular docking techniques. The Stern-Volmer plots and time-resolved fluorescence measurement declared that PMA/TMP quenching the intrinsic fluorescence of BSA/HSA was static quenching process. The binding constants (Ka) and binding sites (n) were calculated at different temperatures. Meanwhile, thermodynamic parameters showed electrostatic forces played a leading role in the interaction of PMA/TMP with BSA/HSA. Some metal ions such as K+, Mg2+, Cu2+, Ca2+, Zn2+ and Fe3+ had no effects on the binding system. The UV-vis absorption spectra confirmed that the interaction between PMA/TMP and BSA/HSA did happen. The analyses of synchronous fluorescence, FT-IR and circular dichroism spectra illustrated that PMA/TMP changed the secondary structures of BSA/HSA. According to Förster non-radiative energy transfer theory, the binding distance between PMA/TMP and BSA/HSA was calculated. The binding location of PMA/TMP to BSA/HSA was identified as sub-domain IIA, which was further confirmed by molecular docking.Communicated by Ramaswamy H. Sarma.

Depicting the binding of furazolidone/furacilin with DNA by multiple spectroscopies, voltammetric as well as molecular docking.

The interaction between DNA and furazolidone/furacillin was investigated using various analytical techniques including spectroscopy and electroanalysis and molecular modelling. With the aid of acridine orange (AO), the fluorescence lifetimes of DNA-AO, DNA-furazolidone/furacillin-AO remained almost the same, which proved that the ground state complex was formed due to furazolidone/furacillin binding with DNA. Circular dichroism spectra and Fourier transform infrared spectroscopy showed that the second structure of DNA changed. Viscosity experiments presented that relative viscosity of DNA was increased with the increasing concentrations of furazolidone and almost unchanged for furacilin. In addition, the results of melting temperature (Tm ), ionic strength, site competition experiments, cyclic voltammetry, and molecular docking all proved the intercalation binding mode for furazolidone and groove binding mode for furacilin. The binding constants (Ka ) obtained from Wolfe-Shimmer equation were calculated as 3.66 × 104 L mol-1 and 3.95 × 104 L mol-1 for furazolidone-DNA and furacilin-DNA, respectively.

Micronomicin/tobramycin binding with DNA: fluorescence studies using of ethidium bromide as a probe and molecular docking analysis.

Two aminoglycosides, micronomicin (MN), and tobramycin (TB), binding with DNA were studied using various spectroscopic techniques including fluorescence, UV-Vis, FT-IR, and CD spectroscopy coupled with relative viscosity and molecular docking. Studies of fluorescence quenching and time-resolved fluorescence spectroscopy all revealed that MN/TB quenching the fluorescence of DNA-EB belonged to static quenching. The binding constants and binding sites were obtained. The values of ΔH, ΔS, and ΔG suggested that van der Waals force or hydrogen bond might be the main binding force. FT-IR and CD spectroscopy revealed that the binding of MN/TB with DNA had an effect on the secondary structure of DNA. Binding mode of MN/TB with DNA was groove binding which was ascertained by viscosity measurements, CD spectroscopy, ionic strength, melting temperature (Tm), contrast experiments with single stranded (ssDNA), and double stranded DNA (dsDNA). Molecular docking analysis further confirmed that the groove binding was more acceptable result.

Study on the interaction of fisetholz with BSA/HSA by multi-spectroscopic, cyclic voltammetric, and molecular docking technique.

The interaction of fisetholz with bovine serum albumin (BSA) and human serum albumin (HSA) was investigated by multi-spectroscopic, cyclic voltammetric, and molecular docking technique. The results revealed that there was a static quenching of BSA/HSA induced by fisetholz. The binding constants (Ka) and binding sites (n) were calculated at different temperatures (293, 303, and 311 K). The enthalpy change (ΔH) were calculated to be -17.20 kJ mol-1 (BSA) and -18.28 kJ mol-1 (HSA) and the entropy change (ΔS) were calculated to be 35.41 J mol-1 (BSA) and 24.02 J mol-1 (HSA), respectively, which indicated that the interaction between fisetholz and BSA/HSA was mainly by electrostatic attraction. Based on displacement experiments using site probes, indomethacin and ibuprofen, the binding site of fisetholz to BSA/HSA was identified as sub-domain IIIA, which was further confirmed by molecular docking method. There was little effect of K+, Ca2+, Cu2+, Zn2+, and Fe3+ on fisetholz-BSA or fisetholz-HSA complex. The spectra of synchronous fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) all showed that fisetholz binding to BSA/HSA leads to secondary structures change of the two serum albumins. According to the Förster non-radiation energy transfer theory, the binding distance between fisetholz and BSA/HSA was 2.94/4.68 nm. The cyclic voltammetry as a supporting tool also indicated that fisetholz interacted with protein. Communicated by Ramaswamy H. Sarma.

Study on the interaction of amprolium HCl and dinitolmide in animal-derived food products with BSA by multiple spectroscopies and molecular modeling techniques.

Communicated by Ramaswamy H. Sarma.

A sensitive resonance Rayleigh light scattering method for alpinetin using gold nanorods probes.

A sensitive resonance Rayleigh light scattering (RLS) assay for alpinetin was developed based on alpinetin-modified gold nanorods (AuNRs). Alpinetin could interact with AuNRs and formed a new assembly by electrostatic attraction. In pH 7.4 Tris-HCl buffer solution, the assembly of alpinetin-AuNRs showed a sensitive RLS signal. Under optimum conditions, the magnitude of enhanced RLS intensity (ΔIRLS ) was proportional to the concentration of alpinetin over the range 0.027-3.24 µg ml-1 , with a detection limit of 1.79 ng ml-1 (by 3σ). The developed RLS method was successfully applied to the detection of alpinetin in real or synthesized samples. Alpinetin recoveries were 90.4-108.7% with an RSD of 0.82-2.9% (n = 5) for Alpinia katsumadai samples, and 95.1-103.7% with an RSD of 0.28-3.9% (n = 5) for synthesized samples. The results showed that this new approach was convenient, reliable and sensitive.

Characterization of the binding of neomycin/paromomycin sulfate with DNA using acridine orange as fluorescence probe and molecular docking technique.

The binding of neomycin sulfate (NS)/paromomycin sulfate (PS) with DNA was investigated by fluorescence quenching using acridine orange (AO) as a fluorescence probe. Fluorescence lifetime, FT-IR, circular dichroism (CD), relative viscosity, ionic strength, DNA melting temperature, and molecular docking were performed to explore the binding mechanism. The binding constant of NS/PS and DNA was 6.70 × 103/1.44 × 103 L mol-1 at 291 K. The values of ΔHθ, ΔSθ, and ΔGθ suggested that van der Waals force or hydrogen bond might be the main binding force between NS/PS and DNA. The results of Stern-Volmer plots and fluorescence lifetime measurements all revealed that NS/PS quenching the fluorescence of DNA-AO was static in nature. FT-IR indicated that the interaction between DNA and NS/PS did occur. The relative viscosity and melting temperature of DNA were almost unchanged when NS/PS was introduced to the solution. The fluorescence intensity of NS/PS-DNA-AO was decreased with the increase in the ionic strength. For CD spectra of DNA, the intensity of positive band at nearly 275 nm was decreased and that of negative band at nearly 245 nm was increased with the increase in the concentration of NS/PS. The binding constant of NS/PS with double-stranded DNA (dsDNA) was larger than that of NS/PS with single-stranded DNA (ssDNA). From these studies, the binding mode of NS/PS with DNA was evaluated to be groove binding. The results of molecular docking further indicated that NS/PS could enter into the minor groove in the A-T rich region of DNA.