In this work, three fluorescein-labeled DiBP derivatives (tracers) with different chemical structures and spacer bridges were synthesized and purified by thin-layer chromatography (TLC). Compared with the heterologous tracer, the homologous tracer exhibited more affinity to the antibody. What is more, the tracer concentration and the antibody dilution were further evaluated to improve the sensitivity of fluorescence polarization immunoassay (FPIA). On the basis of sensitive antibody and tracer, a rapid and specific FPIA has been established for the detection of DiBP contamination in the romaine lettuce, which has rarely been reported before. Under the optimal conditions, the developed FPIA showed a good detection range from 8.82 to 2152.84 ng/mL, with a detection limit of 1.77 ng/mL. In addition, the cross-reactivity to several compounds structurally related to DiBP was less than 7.37 %. Therefore, DiBP contamination in spiked romaine lettuce samples was detected by FPIA, with the recovery from 88.28 to 119.11 %. Moreover, when compared with high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA), the results analyzed by the developed FPIA shows a strong reliability and a high correlation value of 0.978 and 0.980, respectively. Thus, this data, combined with rapidity and simplicity of the assay, demonstrates that the established FPIA is a suitable method for high throughput screening of DiBP contamination in the romaine lettuce.

Bisphenol A (BPA) is a typical endocrine disruptor. It exists everywhere in the environment for its migration from the products of polycarbonate and epoxy resin. It is feasible to develop a fast and sensitive detection method for the effective monitoring of BPA. In this paper, we utilized the advantages of Ag nanoparticle-modified filter paper and cysteamine hydrochloride (Cys) to establish a surface-enhanced Raman spectroscopy (SERS) detection method of BPA. Good uniformity and more “hot spots” can be afforded with the SERS substrate fabricated by vacuum filtration of Ag nanoparticles on filter papers. Cys was used to catch BPA by the electrostatic interaction between positively charged groups of −NH3+ and hydroxy of BPA. Then, BPA-tailed Cys self-assembled to the surface of SERS substrate. Due to the preconcentration of BPA and high coverage of BPA-tailed Cys on the Ag nanoparticle-decorated filter paper, a highly sensitive detection of BPA in water samples was achieved. The method exhibited a good linear correlation ranging from 0.05 to 20 ng/mL with a limit detection of 0.005 ng/mL. Excellent recoveries in water samples from 90.2 to 121.1% were obtained.

A series of N4-benzylamine-N2-isopropyl-quinazoline-2,4-diamine derivatives has been synthesized and tested for antibacterial activity against five bacterial strains. Twelve different substituents on the N4-benzylamine group have been investigated along with replacement of the quinazoline core (with either a benzothiophene or regioisomeric pyridopyrimidine ring systems). In order to develop structure activity relationships, all derivatives were tested for their antibacterial activities against Escherichia coli and Staphylococcus aureus via Kirby–Bauer assays and minimum inhibitory concentration assays. Eight of the most potent compounds against S. aureus and E. coli were also screened against one strain of methicillin-resistant S. aureus (MRSA), Staphylococcus epidermidis and Salmonella typhimurium to further examine their antibacterial activities. Lead compound A5 showed good activities with MICs of 3.9 μg mL−1 against E. coli, S. aureus and S. epidermidis and 7.8 μg mL−1 against MRSA. Selected front runners were also screened for their DMPK properties in vitro to assess their potential for further development.

Novel Cd-doped ZnO/ZnS core–shell quantum dots (QDs) were successfully synthesized via a simple two-step chemical solution method. The morphologies and structures of the product and the precursor were verified using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The exciton dynamics and fluorescence lifetime were studied by time-resolved photoluminescence spectroscopy (TRPL). The thickness of ZnS was controlled by modifying the concentration of thioacetamide (TAA). As the TAA content was increased, the UV-Vis absorption spectra of these novel QDs red shifted toward longer wavelengths; this shift is attributed to the leakage of excitons from the ZnO core to the ZnS shell. The PL emission spectra of the novel QDs blue shifted toward shorter wavelengths as the TAA content was increased, and when the molar ratio of the Cd-doped ZnO to TAA reached 5:1.5. For these novel QDs, the luminous intensity was observed to significantly increase with increasing Cd content at a Cd doping of 20% or less, and a small red shift in the peak was also observed with increasing Cd content. At appropriate Cd doping and ZnS coating, the absolute quantum yield can reach 21% for Cd-doped ZnO/ZnS QDs from 3% and 8% for undoped ZnO/ZnS and Cd-doped ZnO QDs, respectively. All results indicate that the described synthesis method is appropriate for the preparation of Cd-doped ZnO/ZnS core–shell quantum dots with tunable and highly visible photoluminescence.

In this study, a series of novel ursolic acid (UA) derivatives were designed and synthesized successfully via conjugation of hydrophilic and polar groups at 3-OH and/or 17-COOH position. Molecular docking studies were carried out with the binding of UA and acabose in the active site of α-glucosidase, in order to prove that the hydrophilic/polar moieties can interact with the hydrophobic group of the catalytic pocket and form hydrogen bonds. The bioactivities of these synthesized compounds against α-glucosidase were determined in vitro. Kinetic studies were performed to determine the mechanism of inhibition by compounds 3, 4, 10 and 11. The results indicated that most of the target compounds have significant inhibitory activity, and the compound 3, 4, 10 and 11 were potent inhibitors of α-glucosidase, with the IC50 values of 0.149 ± 0.007, 0.223 ± 0.023, 0.466 ± 0.016 and 0.298 ± 0.021 μM, respectively. These compounds were more potent than parent compound and acarbose. The kinetic inhibition studies revealed that compound 3 and 4 were mix-type inhibitors while compound 10 and 11 were non-competitive inhibitors. Furthermore, the molecular docking studies for these two kinds of compounds suggested that free carboxylic group at either C-3 or C-28 position could remarkably improve inhibitory activity. It is noteworthy that the exploration of relationship between hydrophilic and polar groups of these structures and the hydrophobic group in catalytic pocket is benefited from our rational design of potent α-glucosidase inhibitor.

The diisobutyl phthalate (DiBP) hapten containing an amino group was synthesized successfully, and the polyclonal antibody against 4-amino phthalate–bovine serum albumin (BSA) was developed. On the basis of the polyclonal antibody, a rapid and sensitive indirect competitive fluorescence immunoassay (icFIA) has been established to detect DiBP in edible oil samples for the first time. Under the optimized conditions, the quantitative working range of the icFIA was from 10.47 to 357.06 ng/mL (R2 = 0.991), exhibiting a detection limit of 5.82 ng/mL. In this assay, the specific results showed that other similar phthalates did not significantly interfere with the analysis, with the cross-reactivity less than 1.5%, except for that of DiBAP. Thereafter, DiBP contamination in edible oil samples was detected by icFIA, with the recovery being from 79 to 103%. Furthermore, the reliability of icFIA was validated by gas chromatography–mass spectrometry (GC–MS). Therefore, the developed icFIA is suitable for monitoring DiBP in some edible oil samples.

Based on a sensitive monoclonal antibody against bisphenol A (BPA) and a new tracer named BVA–AMF, a homogeneous fluorescence polarization immunoassay (FPIA) was developed and applied in the determination of bisphenol A in environmental water samples. BVA was selected as the hapten to couple with bovine serum albumin and the conjugate was used as the immunogen for the monoclonal antibody production. Three fluorescein-labeled BVA tracers with different structures (BVA–AMF, BVA–EDF, and BVA–lysFITC) were synthesized. Under the same optimal conditions, BVA–AMF showed the highest sensitivity for FPIA and the detection of BPA exhibited a limit of detection of 5.60 ng mL−1, an IC50 of 140 ng mL−1 and a dynamic range of 11.32–904.21 ng mL−1 approximately. In this assay, several similar compounds were shown of little significantly with the cross-reactivity being less than 0.15%. Four different kinds of water samples were analyzed, with recoveries being 87.91–114.28%. The detection standard curve of BPA exhibited a good linearity (R2 = 0.9913, n = 3). Compared with ELISA and HPLC methods, FPIA showed reliability and a high correlation with ELISA of 0.9964 and HPLC of 0.9971. The proposed immunoassay technique is suitable for detection of BPA in authentic environmental water samples.

To save egg yolk immunoglobulin (IgY) from damage by protease digestion in oral delivery, IgY specific to enterovirus 71 (EV71) was loaded into polypeptide microcapsules by the method of layer-by-layer encapsulation. Porous CaCO3 particles doped with IgY were used as templates which were coated with multilayer poly (L-lysine) (PLL) and poly (L-glutamic acid) (PGA). Then, IgY-loaded polypeptide microcapsules were fabricated after the removal of CaCO3 templates. The alternating adsorption was confirmed by the zeta potential and the successful formation of a multilayer polypeptide (PLL/PGA) shell was visualized by SEM. The influence of the PLL/PGA layer numbers on the IgY sustained release performance was studied in simulated gastric fluid. IgY release could be accurately controlled by adjusting the layer number of the polypeptide shells and only 45% of the IgY was released from 5-bilayer microcapsules in the initial 2 hours. The biological activity of the encapsulated IgY was investigated both in vitro and in vivo. Encapsulated EV71-specific IgY remained highly active and capable of neutralizing EV71 after multilayer polypeptide encapsulation, which provided a promising method to protect EV71-specific IgY in the gastric environment and to specifically release IgY at the target intestinal site for the prevention and control of EV71 infectious diseases.

Unconjugated estriol (uE3) is one of the most important serum markers for prenatal screening. The abnormally low content of uE3 is used as an indicator of fetal DS (Down syndrome) during the second trimester in pregnant women. In the present study, we developed a time-resolved fluoroimmunoassay to detect uE3 by employing microtiter plates with pre-captured primary antibodies. E3-3-CME-BSA (estriol-3-carboxymethyl ether-bovine serum albumin) conjugates served as labels and Eu3+ (europium) as the probe for signal detection. The detection limit of this assay was 0.35 nmol L−1. The within-run and between-run imprecision values for serum control detection were less than 5.0% and 6.0% respectively. The mean recovery was 102.6%. The long-term stability (2–8 °C, 15 months) and thermostability (37 °C, 10 days) were excellent. The uE3 concentrations measured by the present assay in 1168 Chinese maternal serum samples correlated well with those obtained by the chemiluminescence immunoassay assay (r = 0.948). The reference range in normal singleton pregnancies in Southern China was established which provided reference data to adjust the uE3 medians for biochemical screening.

•Graphene oxide (GO) is proposed to be able to quench the fluorescence signal.•β-lactamase aptamer was used to replace the traditional antibody.•Based on aptamer assembled onto GO, a new, sensitive and direct determination of β-lactamase was established.•The established method was verified by ELISA.Fluorescent sensor assay (FSA) was developed by using a fluorescein-labeled aptamer assembled onto Graphene oxide (GO) in order to determine β-lactamase in milk. Under optimal conditions, FSA indicated a detection range from 1 to 46 U/mL with a limit of detection (LOD) of 0.5 U/mL (R2 = 0.999, n = 3). In addition, commercial milk samples tainted with β-lactamase were detected by the established FSA with a recovery rate between 96.04 and 119.67%. Additionally, the reliability and sensitivity of FSA was validated by enzyme-linked immunoassay (ELISA) with a high correlation of 0.993. Thus, these data, combined with the ease and speed of the assay, suggest that the developed FSA may represent a promising method for monitoring β-lactamase contamination in milk.

Unconjugated estriol (uE3) is one of the most important serum markers for prenatal screening. The abnormally low content of uE3 is used as an indicator of fetal DS (Down syndrome) during the second trimester in pregnant women. In the present study, we developed a time-resolved fluoroimmunoassay to detect uE3 by employing microtiter plates with pre-captured primary antibodies. E3-3-CME-BSA (estriol-3-carboxymethyl ether-bovine serum albumin) conjugates served as labels and Eu3+ (europium) as the probe for signal detection. The detection limit of this assay was 0.35 nmol L−1. The within-run and between-run imprecision values for serum control detection were less than 5.0% and 6.0% respectively. The mean recovery was 102.6%. The long-term stability (2–8 °C, 15 months) and thermostability (37 °C, 10 days) were excellent. The uE3 concentrations measured by the present assay in 1168 Chinese maternal serum samples correlated well with those obtained by the chemiluminescence immunoassay assay (r = 0.948). The reference range in normal singleton pregnancies in Southern China was established which provided reference data to adjust the uE3 medians for biochemical screening.

Novel Cd-doped ZnO/ZnS core–shell quantum dots (QDs) were successfully synthesized via a simple two-step chemical solution method. The morphologies and structures of the product and the precursor were verified using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The exciton dynamics and fluorescence lifetime were studied by time-resolved photoluminescence spectroscopy (TRPL). The thickness of ZnS was controlled by modifying the concentration of thioacetamide (TAA). As the TAA content was increased, the UV-Vis absorption spectra of these novel QDs red shifted toward longer wavelengths; this shift is attributed to the leakage of excitons from the ZnO core to the ZnS shell. The PL emission spectra of the novel QDs blue shifted toward shorter wavelengths as the TAA content was increased, and when the molar ratio of the Cd-doped ZnO to TAA reached 5:1.5. For these novel QDs, the luminous intensity was observed to significantly increase with increasing Cd content at a Cd doping of 20% or less, and a small red shift in the peak was also observed with increasing Cd content. At appropriate Cd doping and ZnS coating, the absolute quantum yield can reach 21% for Cd-doped ZnO/ZnS QDs from 3% and 8% for undoped ZnO/ZnS and Cd-doped ZnO QDs, respectively. All results indicate that the described synthesis method is appropriate for the preparation of Cd-doped ZnO/ZnS core–shell quantum dots with tunable and highly visible photoluminescence.