I am a postdoctoral researcher working on the detection of chemical contaminants.
Detection of triclosan contamination in food and environment using core-shell satellite substrates
Triclosan (TCS) is a synthetic antimicrobial compound that has been emerging as a potential environmental and food contaminant in recent years. The widespread use of TCS in consumer products has resulted in human and environment exposure. Recent studies have demonstrated uptake and accumulation of TCS by drinking water and edible plants indicating human exposure to TCS. More and more evidence suggest adverse effects of TCS to human health and environment, raising great public concerns. In September 2016, FDA banned the use of TCS and 18 other chemicals in hand and body washes. However, the existing methods are limited to time-consuming, complicated procedure and sophisticated operating environments. Therefore, it is critically urgent and important to develop a rapid, simple and sensitive method for detecting TCS in environmental and food samples. We have been developing a novel surface-enhanced Raman spectroscopy (SERS) analytical platform for rapid capture and detection of TCS using a silver nanoparticle core-protein satellite substrate. SERS spectra of TCS was first studied by using silver nanoparticle (Ag NP) and further used for direct assay of TCS based on its intrinsic SERS peaks. To improve the detection sensitivity, we constructed an innovative Ag NP core - protein satellite substrate for ligand-assisted detection of TCS. Bovine serum albumin (BSA) protein was first assembled onto the surface of Ag NP core to form core-satellite structure. Based on ligand-molecule interaction, BSA assembled on Ag NP could anchor a large number of TCS molecules close to the surface of Ag NP, producing amplified SERS signals. The capability for the differentiation of TCS and its analogue, triclocarban (TCC) was also evaluated. As low as 50 nM TCS was successfully detected within 30 min. To the best of our knowledge, it will be the first example of studying SERS spectra of TCS and developing SERS-based methods for TCS detection. Our methods will potentially fulfill the urgent need for rapidly detecting TCS in environmental, food and consumer products, and greatly facilitate accurate and reliable assessment of the environmental and human health risks associated with TCS exposure.
Abstract: There are still challenges for the development of multifunctional carbon nanotubes (CNTs). Here, a multiwalled carbon nanotube (MWCNT)-based rolling circle amplification system (CRCAS) is reported which allows in situ rolling circle replication of DNA primer on the surface of MWCNTs to create a long single-strand DNA (ssDNA) where a large number of nanoparticles or proteins could be loaded, forming a nano-biohybridized 3D structure with a powerful signal amplification ability. In this strategy, the binding ability of proteins, hybridization, replication ability of DNA, and the catalytical ability of enzymes are integrated on a single carbon nanotube. The CRCAS is then used to develop colorimetric and chemiluminescent assays for the highly sensitive and specific detection of cancer protein markers, alpha-fetoprotein (AFP) and prostate specific antigen (PSA). The colorimetric CRCAS assay is 4000 times more sensitive than a conventional enzyme-linked immunosorbent assay (ELISA), and its concentration range is 10,000 times wider. Control experiments show that as low as 10 pg mL⁻¹ AFP or PSA could be detected even in the presence of interfering protein markers with a more than 10⁵-fold greater concentration in the sample, demonstrating the high specificity of the CRCAS assay. The limit of detection of the chemiluminescent CRCAS assays for AFP and PSA are 5 fg mL⁻¹ (70 aM) and 10 fg mL⁻¹ (0.29 fM), respectively, indicating that the sensitivity is much higher than that of the colorimetric CRCAS assay. Importantly, CRCAS works well with real biological samples.
Pub.: 19 Mar '13, Pinned: 01 Aug '17
Abstract: Microarrays of biomolecules have greatly promoted the development of the fields of genomics, proteomics, and clinical assays because of their remarkably parallel and high-throughput assay capability. Immobilization strategies for biomolecules on a solid support surface play a crucial role in the fabrication of high-performance biological microarrays. In this study, rationally designed DNA tetrahedra carrying three amino groups and one single-stranded DNA extension were synthesized by the self-assembly of four oligonucleotides, followed by high-performance liquid chromatography purification. We fabricated DNA tetrahedron-based microarrays by covalently coupling the DNA tetrahedron onto glass substrates. After their biorecognition capability was evaluated, DNA tetrahedron microarrays were utilized for the analysis of different types of bioactive molecules. The gap hybridization strategy, the sandwich configuration, and the engineering aptamer strategy were employed for the assay of miRNA biomarkers, protein cancer biomarkers, and small molecules, respectively. The arrays showed good capability to anchor capture biomolecules for improving biorecognition. Addressable and high-throughput analysis with improved sensitivity and specificity had been achieved. The limit of detection for let-7a miRNA, prostate specific antigen, and cocaine were 10 fM, 40 pg/mL, and 100 nM, respectively. More importantly, we demonstrated that the microarray platform worked well with clinical serum samples and showed good relativity with conventional chemical luminescent immunoassay. We have developed a novel approach for the fabrication of DNA tetrahedron-based microarrays and a universal DNA tetrahedron-based microarray platform for the detection of different types of bioactive molecules. The microarray platform shows great potential for clinical diagnosis.
Pub.: 10 Oct '14, Pinned: 01 Aug '17
Abstract: Isothermal amplification is an efficient way to amplify DNA with high accuracy, however, the real-time monitoring for quantification analysis mostly relied on expensive and precisely designed probes. In the present study, Graphene oxide (GO)-based nano probe was used to real-time monitor the isothermal amplification process. The interaction between GO and different DNA structures was systematically investigated, including single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), DNA 3-helix, and long rolling circle amplification (RCA) and hybridization chain reaction (HCR) products, which existed in one-, two- and three-dimensional structures. It was found that the high rigid structures exhibited much lower affinity with GO than soft ssDNA, and generally the rigidity was dependent on the length of targets and the hybridization position with probe DNA. Based on these results, we successfully monitored HCR amplification process, RCA process and the enzyme restriction of RCA products with GO nanoprobe, other application including the detection of the assembly/disassembly of DNA 3-helix structures were also performed. Compared to the widely used end-point detection methods, the GO-based sensing platform is simple, sensitive, cost-effective, and especially in a real-time monitoring mode. We believe such studies can provide comprehensive understandings and evocation on design of GO-based biosensors for broad application in various fields.
Pub.: 18 Apr '17, Pinned: 01 Aug '17
Abstract: Understanding pesticide behavior in plants is important for effectively applying pesticides and in reducing pesticide exposures from the ingestion. This study aimed to investigate the penetration and persistence of pesticides applied on harvested and live basil leaves. Surface-enhanced Raman scattering (SERS) mapping was applied for in situ and real-time tracking of pesticides over time using gold nanoparticles as probes. The results showed that after surface exposure of 30 min to 48 h, pesticides (10 mg/L) penetrated more rapidly and deeply into the live leaves than the harvested leaves. Systemic pesticide thiabendazole and the non-systemic pesticide ferbam can penetrate into the live leaves with depth of 225 μm and 130 μm, respectively than the harvested leaves with depth of 180 μm and 18 μm, respectively after 48-h exposure. The effects of leaf integrity and age on thiabendazole penetration were also evaluated on live basil leaves after 24-h exposure. Thiabendazole (10 mg/L) when applied onto intact leaves penetrated deeper (170 μm) than when applied onto damaged leaves (80 μm) prepared with 20 scrapes on the top surface of leaves. Older leaves with a wet mass of 0.204 ± 0.019 g per leaf (45 days after leaf out) allowed more rapid and deeper penetration of pesticides (depth of 165 μm) than when younger leaves with a wet mass of 0.053 ± 0.007 g per leaf (15 days after leaf out) were used (depth of 95 μm). The degradation of thiabendazole on live leaves was detected after 1 week whereas the apparent degradation of ferbam was detected after 2 weeks. In addition, the removal of pesticides from basil was more efficient when compared with other fresh produce possibly due to the specific gland structure of basil leaves. The information obtained here provides a better understanding of the behavior and biological fate of pesticides on plants.
Pub.: 11 Apr '17, Pinned: 01 Aug '17
Abstract: Uniform silver-containing metal nanostructures with well-defined nanogaps hold great promise for ultrasensitive surface-enhanced Raman scattering (SERS) analyses. Nevertheless, the direct synthesis of such nanostructures with strong and stable SERS signals remains extremely challenging. Here, we report a DNA-mediated approach for the direct synthesis of gold-silver nano-mushrooms with interior nanogaps. The SERS intensities of these nano-mushrooms were critically dependent on the area of the nanogap between the gold head and the silver cap. We found that the formation of nanogaps was finely tunable by controlling the surface density of 6-carboxy-X-rhodamine (ROX) labeled single-stranded DNA (ssDNA) on the gold nanoparticles. We obtained nano-mushrooms in high yield with a high SERS signal enhancement factor of ∼1.0 × 109, much higher than that for Au-Ag nanostructures without nanogaps. Measurements for single nanomushrooms show that these structures have both sensitive and reproducible SERS signals.
Pub.: 13 Sep '14, Pinned: 01 Aug '17
Abstract: Although "hot spots" have been proved to contribute to surface enhanced Raman scattering (SERS), less attention was paid to increase the number of the "hot spot" to directly enhance the Raman signals in bioanalytical systems. Here we report a new strategy based on nano rolling-circle amplification (nanoRCA) and nano hyperbranched rolling-circle amplification (nanoHRCA) to increase "hot spot" groups for protein microarrays. First, protein and ssDNA are coassembled on gold nanoparticles, making the assembled probe have both binding ability and hybridization ability. Second, the ssDNAs act as primers to initiate in situ RCA reaction to produced long ssDNAs. Third, a large number of SERS probes are loaded on the long ssDNA templetes, allowing thousands of SERS probes involved in each biomolecular recognition event. The strategy offered high-efficiency Raman enhancement and could detect less than 10 zeptomolar protein molecules in protein microarray analysis.
Pub.: 11 Oct '12, Pinned: 01 Aug '17
Abstract: Understanding of the penetration behaviors of pesticides in fresh produce is of great significance for effectively applying pesticides and minimizing pesticide residues in food. There is lack, however, of an effective method that can measure pesticide penetration. Herein, we developed a novel method for real-time and in situ monitoring of pesticide penetration behaviors in spinach leaves based on surface-enhanced Raman scattering (SERS) mapping. Taking advantage of penetrative gold nanoparticles (AuNPs) as probes to enhance the internalized pesticide signals in situ, we have successfully obtained the internal signals from thiabendazole, a systemic pesticide, following its penetration into spinach leaves after removing surface pesticide residues. Comparatively, ferbam, a nonsystemic pesticide, did not show internal signals after removing surface pesticide residues, demonstrating its nonsystemic behavior. In both cases, if the surface pesticides were not removed, copenetration of both AuNPs and pesticides was observed. These results demonstrate a successful application of SERS as an effective method for measuring pesticides penetration in fresh produce in situ. The information obtained could provide useful guidance for effective and safe applications of pesticides on plants.
Pub.: 21 Apr '16, Pinned: 01 Aug '17
Abstract: Molecular computing holds great promise for diagnosis and treatment of diseases at the molecular level; nevertheless, designing molecular logic gates to operate programmably and autonomously for molecular diagnostics still remains challenging. We designed logic gates on DNA Origami for microRNA analysis. As a demonstration, two indicators of heart failure, microRNA-21 and microRNA-195, were selected as the logic inputs. The logic gates contain two main modules: computation module and output module, performing in a single DNA Origami nanostructure. The computation module recognizes disease indicators, while the output module display different nanoscale symbols, "+" (positive) or "-" (negative), depending on the computing results. We demonstrated that the molecular logic gates worked well with single and two input combinations.
Pub.: 23 Jan '14, Pinned: 01 Aug '17
Abstract: Several single-stranded scaffold DNA, obtained from rolling circle amplification (RCA), are folded by different staples to form DNA nanoribbons. These DNA nanoribbons are rigid, simple to design, and cost-effective drug carriers, which are readily internalized by mammalian cells and show enhanced immunostimulatory activity.
Pub.: 25 Apr '13, Pinned: 01 Aug '17