Baoan Ning

Development of gold nanoparticle-based rapid detection kit for melamine in milk products.

A reliable and sensitive kit for the rapid detection of melamine (Mel) was developed. The kit is based on gold nanoparticle (Au NP) probe and includes a standard colorimetric card. The Au NPs were prepared by sodium borohydride reduction and characterized by transmission electron microscopy, which revealed particle sizes of approximately 5 nm. The performance of the kit in terms of aggregation kinetics, cross-reactivity, anti-interference, and sample pretreatment was investigated. The standard colorimetric card was then fabricated by chromatic aberration of a series of standard Mel-spiked milk reacts with the 5 nm Au NPs. The working range of the kit is 1-120 mg/L, and its performance is visibly more rapid and reliable by comparison with the standard colorimetric card. As low as 1 mg/L of Mel levels in milk can be determined, with the assay taking only about 10 min, including sample pretreatment. The kit can be stored for a year at room temperature. Samples were also detected by the kit, yielding results close to those obtained by high-performance liquid chromatography/mass spectrometry. Thus, the kit is applicable to qualitative and semiquantitative field detection, as well as naked-eye screening without the aid of any instrumentation.

Molecularly imprinted photonic polymer as an optical sensor to detect chloramphenicol

An inverse opal photonic crystal sensor that could specifically detect chloramphenicol (CAP) in a label-free way was introduced in the current research. A colloidal crystal template was first prepared from monodisperse SiO(2) nanospheres. Precursors with different compositions were infused into the void spaces of the respective templates and aggregated. The template and the imprinted CAP were removed, and a molecularly imprinted photonic polymer (MIPP) with numerous nanocavities derived from the SiO(2) template was prepared. The MIPP could specifically recognize the target CAP. The results showed that the embedding and transporting of CAP could change the reflection peak intensity of the MIPP. The MIPP exhibited good responsiveness, with a detection range from 1 ng mL(-1) to 1 μg mL(-1) of CAP. The MIPP response time was 8 min upon its addition to CAP at a concentration of 10 ng mL(-1), which is shorter than that of other methods. After repeated use, the MIPP maintained a good performance and detection capacity. Thus, the results prove that the novel sensor could specifically detect CAP in a simple, time-saving, and low-cost manner.

Sensitive detection of atrazine in tap water using TELISA.

A highly sensitive flow injection analysis (FIA)-based thermal enzyme-linked immunoassay, TELISA, was developed for the rapid detection of atrazine (ATZ) in tap water. ATZ and β-lactamase-labeled ATZ were employed in a competitive immunoassay using a monoclonal antibody (mAb). After the off-column liquid-phase competition, the mAb was captured on the Protein G Sepharose™ 4 Fast Flow (PGSFF) column support material. Injected β-lactamase substrate ampicillin was degraded by the column-bound ATZ-β-lactamase, generating a detectable heat signal. Several assay parameters were optimized, including substrate concentration, flow rates and regeneration conditions, as well as the mAb and ATZ-β dilution ratios and concentrations. The assay linear range was 0.73-4.83 ng mL(-1) with a detection limit of 0.66 ng mL(-1). An entire heat signal requires 10 min for generation, and the cycle time is less than 40 min. The results were reproducible and stable. ATZ-spiked tap water samples exhibited a recovery rate of 103%-116%, which correlated with the UHPLC-MS/MS measurements. We attributed this significant increase in sensitivity over our previously published work to the following factors: (i) the capture of already-formed immune complexes on the column via immobilized Protein G, which eliminated chemical immobilization of the antibody; (ii) off-column preincubation allows the formation of immune complexes under nearly ideal conditions; and (iii) multiple buffers can be used to, in one case, enhance immune-complex formation and in the other to maximize enzymatic activity. Furthermore, the scheme creates a universal assay platform in which sensing is performed in the off-column incubation and detection after capture in the enzyme thermistor (ET) detector, which opens up the possibility of detecting any antigen for which antibodies were available.

A label-free detection of diethylstilbestrol based on molecularly imprinted polymer-coated upconversion nanoparticles obtained by surface grafting

Herein, we report a novel fluorescent sensor based on molecularly imprinted polymer-coated upconversion nanoparticles (MIP-coated UCNPs) for the recognition and detection of diethylstilbestrol (DES). We used one-step process to modify the surface of the UCNPs with alkenyl groups, which was not only a simple process, but also greatly saved the preparation time. Then, a molecularly imprinted polymer was synthesized on the UCNPs by the surface-graft molecular imprinting method. MIP-coated UCNPs combine the advantages of UCNPs and molecularly imprinted polymers such as strong fluorescence properties, excellent stability, reusability, good adsorption capacity, and high specificity. After the removal of the template molecules, the UCNPs were able to selectively recognize DES, and the fluorescence intensity decreased as the concentration of DES increased. A good linear relationship was obtained in the concentration range of 50–1000 ng mL−1 with the correlation coefficient of 0.9989, and the detection limit was 12.8 ng mL−1 (S/N = 3). MIP-coated UCNPs could be applied for the detection of DES in real milk samples, and the average recoveries for five different concentrations ranged from 90.3% to 107.8%, with the relative standard deviations (RSD) below 2.7%. This fluorescence sensor provides a more convenient, simple and highly specific method for the on-field detection of DES and is promising for a wide range of applications in the future.

High-throughput suspension array for detecting four pathogens

A new suspension array technology is proposed for the simultaneous quantitative determination of four pathogens in food. Four sets of primers and species-specific capture probes were designed based on the 16S rDNA gene sequences of Escherichia coli, Staphylococcus aureus, Vibrio parahaemolyticus, and Salmonella downloaded from GenBank. The specific nucleic acid probes were covalently bound to the surface of fluorescent microspheres for liquid suspension hybridization. The biotin-labeled PCR products obtained from the samples were hybridized with their complementary nucleic acid probes, which were detected after the addition of streptavidin phycoerythrin. No cross-reaction occurred among the products, and the sensitivity of the probe in the single-channel method was 5 × 10−6 mM. In the multi-channel method, the sensitivities were as follows: 5 × 10−4 mM for E. coli and Salmonella, and 5 × 10−5 mM for S. aureus and V. parahaemolyticus. The multi-channel method achieved multidetection of several pathogens. For real sample detection, the methods showed a sensitivity of 103 CFU per g to 100 CFU per g of vegetables after enrichment for 24 h at 37 °C. This study demonstrates the utility of the suspension array specific for the 16S rDNA gene for determining the presence of the four pathogens in food samples.

Novel Biomimic Crystalline Colloidal Array for Fast Detection of Trace Parathion

A novel gold doped inverse opal photonic crystal (IO PC) was successfully fabricated with combination of molecularly imprinted technical for the fast determination of parathion. First, a closest silica array arrangement behaved as the 3D photonic crystal precursors to build the opal photonic crystal (O PC). Second, the parathion-containing polymeric solution with gold nanoparticles was drawn into the 3D array cracks. After polymerization, the well-designed O PC was treated with HF solution for the etching of the silica skeleton. Finally, the template parathion was removed and the Au-MIP IO PCs were obtained. The morphology of SiO2 and Au NPs was characterized by transmission electron microscopy (TEM), and the eluted influence of the IO PCs was monitored by scanning electron microscopy (SEM). The cross-linking effect was well optimized according to the best spectrum signal of parathion. The as-synthesized Au-MIP IO PCs displayed the specificity toward parathion and the selectivity to other competitive pesticide molecules. The response time was only 5 min, and the parathion could be well detected from real water samples. The recoveries were between 95.5% and 101.5%.

An upconversion fluorescent aptasensor for polychlorinated biphenyls detection based on nicking endonuclease and hybridization chain reaction dual-amplification strategy

A novel upconversion fluorescent aptasensor based on hybridization chain reaction and nicking endonuclease has been developed for detection of polychlorinated biphenyls (PCBs). It combined the dual advantages of UCNPs and HCR. Two harpins (H1 and H2) were first designed according to the partial complementary sequence (cDNA) of the PCB72/106. Since the aptamer specifically recognized the target, the cDNA was detached from the magnetic microspheres (MMPs). The cDNA could initiate hybridization chain reaction (HCR) and open the stems of H1 and H2. After the addition of nicking endonuclease, UCNPs were further away from the quenchers (BHQ-1). Hence, the fluorescence intensity of upconversion nanoparticals (UCNPs) could be restored via fluorescence resonance energy transfer (FRET). Therefore, the fluorescence of UCNPs was directly proportional to concentration of PCB72/106, which was the basis for the quantification of PCB72/106. PCB72/106 could be analyzed within the ranges of 0.004 to 800 ng/mL with a detection limit of 0.0035 ng/mL ( S/ N = 3). The aptasensor was also used for the detection of water and soil samples, and the average recoveries ranged from 93.4% to 109.7% and 83.2% to 118.5%, respectively. The relative standard deviations (RSDs) were all below 3.2%. The signal was first amplified through HCR and further amplified with the help of nicking endonuclease. This work also provided the opportunity to develop fluorescent aptasensors for other targets using this dual-amplification strategy.

Ultrasensitive detection of T-2 toxin in food based on bio-barcode and rolling circle amplification

A novel and highly sensitive method based on bio-barcode with rolling circle amplification (RCA) was developed for the detection of T-2 toxin. Gold nanoparticles (AuNPs) were modified with anti-T-2 monoclonal antibody and single-stranded thiol-oligonucleotides (SH-ssDNAs) and magnetic microparticles (MMPs) coated with T-2 antigen. The T-2 toxin competes with the antigen on MMPs for the anti-T-2 antibody on AuNPs. Then, the isolating complex system was separated by a magnetic field, and the DNA of the probes was released after washing in dithiothreitol solution. The barcode DNA via RCA and products were stained by SYBR Green I and then detected by fluorescence spectrophotometry. The optimized method was performed on oats, millet, flour, and other substances. This method exhibits a low limit of detection (0.26 pg mL-1) and linear range of 0.002-200 ng mL-1. Moreover, the approach offers good recovery and relative standard deviations ranging from 88.65% to 10.04% and 0.6%-13.1%, respectively. In conclusion, this method exhibits potential for use as an ultrasensitive assay for the detection of a variety of small molecules in complex matrices.

Ultrasensitive Sensing Material Based on Opal Photonic Crystal for Label-Free Monitoring of Transferrin

A new opal photonic crystal (PC) sensing material, allowing label-free detection of transferrin (TRF), is proposed in the current study. This photonic crystal was prepared via a vertical convective self-assembly method with monodisperse microspheres polymerized by methyl methacrylate (MMA) and 3-acrylamidophenylboronic acid (AAPBA). FTIR, TG, and DLS were used to characterize the components and particle size of the monodisperse microspheres. SEM was used to observe the morphology of the PC. The diffraction peak intensity decreases as the TRF concentration increase. This was due to the combination of TRF to the boronic acid group of the photonic crystal. After condition optimization, a standard curve was obtained and the linear range of TRF concentration was from 2 × 10-3 ng/mL to 200 ng/mL. Measurement of TRF concentration in simulated urine sample was also investigated using the sensing material. The results indicated that the PC provided a cheap, label-free, and easy-to-use alternative for TRF determination in clinical diagnostics.