Showing papers by "Xingyu Jiang published in 2012"
TL;DR: This investigation would allow the development of antibacterial agents that target the energy-metabolism and transcription of bacteria without triggering the ROS reaction, which may be at the same time harmful for the host when killing bacteria.
630 citations
TL;DR: This report presents a highly sensitive, rhodamine B-covered gold nanoparticle (RB-AuNP) -based assay with dual readouts (colorimetric and fluorometric) for detecting organophosphorus and carbamate pesticides in complex solutions.
Abstract: This report presents a highly sensitive, rhodamine B-covered gold nanoparticle (RB-AuNP) -based assay with dual readouts (colorimetric and fluorometric) for detecting organophosphorus and carbamate pesticides in complex solutions. The detection mechanism is based on the fact that these pesticides can inhibit the activity of acetylcholinesterase (AChE), thus preventing the generation of thiocholine (which turns the RB-AuNP solutions blue and unquenches the fluorescence of RB simultaneously). The color of the RB-AuNP solution remains red and the fluorescence of RB remains quenched. By use of this dual-readout assay, the lowest detectable concentrations for several kinds of pesticides including carbaryl, diazinon, malathion, and phorate were measured to be 0.1, 0.1, 0.3, and 1 μg/L, respectively, all of which are much lower than the maximum residue limits (MRL) as reported in the European Union pesticides database as well as those from the U.S. Department Agriculture (USDA). This assay allows detection of pe...
379 citations
TL;DR: This work reports on a passive double spiral microfluidic device allowing rapid and label-free tumor cell separation and enrichment from diluted peripheral whole blood, by exploiting the size-dependent hydrodynamic forces.
Abstract: This work reports on a passive double spiral microfluidic device allowing rapid and label-free tumor cell separation and enrichment from diluted peripheral whole blood, by exploiting the size-dependent hydrodynamic forces. A numerical model is developed to simulate the Dean flow inside the curved geometry and to track the particle/cell trajectories, which is validated against the experimental observations and serves as a theoretical foundation for optimizing the operating conditions. Results from separating tumor cells (MCF-7 and Hela) spiked into whole blood indicate that 92.28% of blood cells and 96.77% of tumor cells are collected at the inner and the middle outlet, respectively, with 88.5% tumor recovery rate at a throughput of 3.33 × 107 cells min−1. We expect that this label-free microfluidic platform, driven by purely hydrodynamic forces, would have an impact on fundamental and clinical studies of circulating tumor cells.
259 citations
TL;DR: The fabrication of tubular structures, with multiple cell types forming different layers of the tube walls, is described using a stress-induced rolling membrane (SIRM).
Abstract: The fabrication of tubular structures, with multiple cell types forming different layers of the tube walls, is described using a stress-induced rolling membrane (SIRM). Cell orientation inside the tubes can also be controlled by topographical contact guidance. These layered tubes precisely mimic blood vessels and many other tubular structures, suggesting that they may be of great use in tissue engineering.
225 citations
TL;DR: This microfluidic flow-stretch chip integrates fluid shear stress (FSS) and cyclic stretch (CS), two major mechanical stimulations in cardiovascular systems, for cultured cells to mimic the haemodynamic microenvironment of blood vessels in vivo.
Abstract: This microfluidic flow-stretch chip integrates fluid shear stress (FSS) and cyclic stretch (CS), two major mechanical stimulations in cardiovascular systems, for cultured cells. The model chip can deliver FSS and CS simultaneously or independently to vascular cells to mimic the haemodynamic microenvironment of blood vessels in vivo. By imposing FSS-only, CS-only, and FSS+CS stimulation on rat mesenchymal stem cells and human umbilical vein endothelial cells, we found the alignment of the cellular stress fibers varied with cell type and the type of stimulation. The flow-stretch chip is a reliable tool for simulating the haemodynamic microenvironment.
120 citations
TL;DR: It is found that the fluorescent gold nanoparticles could selectively detect copper ions in aqueous solution, with a limit of detection of about 87 nM.
Abstract: A simple and one-pot method for the synthesis of water-soluble, red-emitting, highly fluorescent gold nanoparticles has been reported using 11-mercaptoundecanoic acid (11-MUA) as the protecting group. We found that the fluorescent gold nanoparticles could selectively detect copper ions in aqueous solution, with a limit of detection of about 87 nM.
108 citations
TL;DR: A simple method of cell patterning, inspired by the mussel anchoring protein, is introduced and the combination of PDA and PEG enables us to make cell patterns on common laboratorial materials in a mild and convenient fashion.
Abstract: This Article introduces a simple method of cell patterning, inspired by the mussel anchoring protein. Polydopamine (PDA), artificial polymers made from self-polymerization of dopamine (a molecule that resembles mussel-adhesive proteins), has recently been studied for its ability to make modifications on surfaces in aqueous solutions. We explored the interfacial interaction between PDA and poly(ethylene glycol) (PEG) using microcontact printing (μCP). We patterned PDA on several substrates such as glass, polystyrene, and poly(dimethylsiloxane) and realized spatially defined anchoring of mammalian cells as well as bacteria. We applied our system in investigating the relationship between areas of mammalian nuclei and that of the cells. The combination of PDA and PEG enables us to make cell patterns on common laboratorial materials in a mild and convenient fashion.
88 citations
TL;DR: A highly sensitive, selective, and dual-readout (colorimetric and fluorometric) assay for acetylcholinesterase (AChE) based on Rhodamine B-modified gold nanoparticle is reported, which can be used for monitoring AChE levels in the cerebrospinal fluid of transgenic mice with Alzheimer's disease.
Abstract: A highly sensitive, selective, and dual-readout (colorimetric and fluorometric) assay for acetylcholinesterase (AChE) based on Rhodamine B-modified gold nanoparticle is reported. Due to its good sensitivity and selectivity, the assay can be used for monitoring AChE levels in the cerebrospinal fluid of transgenic mice with Alzheimer's disease.
86 citations
TL;DR: This letter presents a click-chemistry-based assay for proteins (CAP) that allows quantitative determination of the concentration of proteins, using azide- and alkyne-functionalized gold nanoparticles (AuNPs).
Abstract: This letter presents a click-chemistry-based assay for proteins (CAP) that allows quantitative determination of the concentration of proteins, using azide- and alkyne-functionalized gold nanoparticles (AuNPs). Compared with conventional methods, CAP has a broader linear range for detection of proteins with good selectivity. CAP enables the analysis of total proteins in various sera and milk samples.
80 citations
TL;DR: This work developed a portable integrated microchip of loop-mediated isothermal nucleic acid amplification (LAMP), namely integrated micro-LAMP, which was successfully used for point-of-care identification of bacteria.
Abstract: In this work, we developed a portable integrated microchip of loop-mediated isothermal nucleic acid amplification (LAMP). This chip, with sample-to-answer capability, could perform rapid DNA release, exponential signal amplification and naked-eye result read-out in single or multiplex format. We call it iμLAMP, namely integrated micro-LAMP, which was successfully used for point-of-care identification of bacteria.
80 citations
TL;DR: Laminin/Itgb1 signaling plays an instructive role in axon initiation and growth, both in vitro and in vivo, through the regulation of microtubule assembly, and a linkage between an extrinsic factor and intrinsic cytoskeleton dynamics during neuronal polarization is established.
Abstract: Axon specification during neuronal polarization is closely associated with increased microtubule stabilization in one of the neurites of unpolarized neuron, but how this increased microtubule stability is achieved is unclear. Here, we show that extracellular matrix (ECM) component laminin promotes neuronal polarization via regulating directional microtubule assembly through β1 integrin (Itgb1). Contact with laminin coated on culture substrate or polystyrene beads was sufficient for axon specification of undifferentiated neurites in cultured hippocampal neurons and cortical slices. Active Itgb1 was found to be concentrated in laminin-contacting neurites. Axon formation was promoted and abolished by enhancing and attenuating Itgb1 signaling, respectively. Interestingly, laminin contact promoted plus-end microtubule assembly in a manner that required Itgb1. Moreover, stabilizing microtubules partially prevented polarization defects caused by Itgb1 downregulation. Finally, genetic ablation of Itgb1 in dorsal telencephalic progenitors caused deficits in axon development of cortical pyramidal neurons. Thus, laminin/Itgb1 signaling plays an instructive role in axon initiation and growth, both in vitro and in vivo, through the regulation of microtubule assembly. This study has established a linkage between an extrinsic factor and intrinsic cytoskeletal dynamics during neuronal polarization.
TL;DR: A recyclable Hg(2+) probe based on Rhodamine B isothiocyanate (RBITC)-poly(ethylene glycol) (PEG)-comodified gold nanoparticles (AuNPs) with excellent robustness, selectivity, and sensitivity that can be regenerated by resupplying free RBITC into the AuNPs solutions that were already used for detecting HG(2+).
Abstract: We designed a recyclable Hg2+ probe based on Rhodamine B isothiocyanate (RBITC)-poly(ethylene glycol) (PEG)-comodified gold nanoparticles (AuNPs) with excellent robustness, selectivity, and sensitivity. On the basis of a rational design, only Hg2+ can displace RBITC from the AuNP surfaces, resulting in a remarkable enhancement of RBITC fluorescence initially quenched by AuNPs. To maintain stability and monodispersity of AuNPs in real samples, thiol-terminated PEG was employed to bind with the remaining active sites of AuNPs. Besides, this displacement assay can be regenerated by resupplying free RBITC into the AuNPs solutions that were already used for detecting Hg2+. Importantly, the detection limit of this assay for Hg2+ (2.3 nM) was lower than the maximum limits guided by the United States Environmental Protection Agency as well as that permitted by the World Health Organization. The efficiency of this probe was demonstrated in monitoring Hg2+ in complex samples such as river water and living cells.
TL;DR: By quantitatively comparing a variety of macromolecular surface coating agents, it is discovered that surface coating strongly modulates the adhesion and morphogenesis of primary hippocampal neurons and serves as a switch of somata clustering and neurite fasciculation in vitro.
Abstract: By quantitatively comparing a variety of macromolecular surface coating agents, we discovered that surface coating strongly modulates the adhesion and morphogenesis of primary hippocampal neurons and serves as a switch of somata clustering and neurite fasciculation in vitro. The kinetics of neuronal adhesion on poly-lysine-coated surfaces is much faster than that on laminin and Matrigel-coated surfaces, and the distribution of adhesion is more homogenous on poly-lysine. Matrigel and laminin, on the other hand, facilitate neuritogenesis more than poly-lysine does. Eventually, on Matrigel-coated surfaces of self-assembled monolayers, neurons tend to undergo somata clustering and neurite fasciculation. By replacing coating proteins with cerebral astrocytes, and patterning neurons on astrocytes through self-assembled monolayers, microfluidics and micro-contact printing, we found that astrocyte promotes soma adhesion and astrocyte processes guide neurites. There, astrocytes could be a versatile substrate in engineering neuronal networks in vitro. Besides, quantitative measurements of cellular responses on various coatings would be valuable information for the neurobiology community in the choice of the most appropriate coating strategy.
TL;DR: An integrated platform combining localized-surface plasmon resonance (LSPR) and microfluidic chips to carry out multiplexed and label-free protein analysis is reported.
Abstract: This work reports an integrated platform combining localized-surface plasmon resonance (LSPR) and microfluidic chips to carry out multiplexed and label-free protein analysis. We fabricated an optical bench to enable detection using only a laboratory UV-Vis spectrophotometer. This assay not only improves throughput, but also allows quantitative analysis.
TL;DR: It is reported that the signals of the purinergic (P)2X3 receptor, an ATP-gated ion channel, are retrogradely transported in dorsal root ganglion (DRG) neuron axons and found that Rab5, a small GTPase, controls the early sorting of P2x3 receptors into endosomes, while Rab7 mediates the fast retrograde transport of P 2X3 receptors.
Abstract: Neurotrophins and their receptors adopt signaling endosomes to transmit retrograde signals. However, the mechanisms of retrograde signaling for other ligand/receptor systems are poorly understood. Here, we report that the signals of the purinergic (P)2X(3) receptor, an ATP-gated ion channel, are retrogradely transported in dorsal root ganglion (DRG) neuron axons. We found that Rab5, a small GTPase, controls the early sorting of P2X(3) receptors into endosomes, while Rab7 mediates the fast retrograde transport of P2X(3) receptors. Intraplantar injection and axonal application into the microfluidic chamber of alpha, beta-methylene-ATP (alpha, beta-MeATP), a P2X selective agonist, enhanced the endocytosis and retrograde transport of P2X(3) receptors. The alpha, beta-MeATP-induced Ca2+ influx activated a pathway comprised of protein kinase C, rat sarcoma viral oncogene and extracellular signal-regulated protein kinase (ERK), which associated with endocytic P2X(3) receptors to form signaling endosomes. Disruption of the lipid rafts abolished the alpha, beta-MeATP-induced ERK phosphorylation, endocytosis and retrograde transport of P2X(3) receptors. Furthermore, treatment of peripheral axons with alpha, beta-MeATP increased the activation level of ERK and cAMP response element-binding protein in the cell bodies of DRG neurons and enhanced neuronal excitability. Impairment of either microtubule-based axonal transport in vivo or dynein function in vitro blocked alpha, beta-MeATP-induced retrograde signals. These results indicate that P2X(3) receptor-activated signals are transmitted via retrogradely transported endosomes in primary sensory neurons and provide a novel signaling mechanism for ligand-gated channels.
TL;DR: A casein assay has been developed with aggregation induced emission character of BSPOTPE, which is a derivative of tetraphenylethene (TPE), and can detect the casein in skimmed and full milk powder, avoiding the interferences from other components and illegal additives in milk.
Abstract: A casein assay has been developed with aggregation induced emission character of BSPOTPE, which is a derivative of tetraphenylethene (TPE). The method exhibits a wide dynamic range of detection for casein from 10 μg ml−1 to 5000 μg ml−1, and a good linear range from 20 μg ml−1 to 1250 μg ml−1. With sample-pretreatment procedures, we can detect the casein in skimmed and full milk powder, avoiding the interferences from other components and illegal additives in milk.
TL;DR: This study found that rat mesenchymal stem cells (rMSCs) presented a contraction and re-spread (CRS) process when they were initially subjected to a physiological FSS (1.3 Pa) and revealed the immediate response of the rMSCs to FSS.
Abstract: Mesenchymal stem cells (MSCs), the multipotent progenitor cells, are sensitive to fluid shear stress (FSS). MSCs can migrate through the blood stream by intravasation into the circulatory system to transfer to distant positions through the blood stream. During the transferring process, MSCs may differentiate into cells of corresponding tissues for repair, or remain undifferentiated and initiate ectopic tissue formation, lipid accumulation, or calcification, which are closely related to the pathology of atherosclerosis. However, how the MSCs sense and respond to vascular FSS stimulation and lead to subsequent biological effects remains elusive. In this study, by using an in situ time-lapse microfluidic cell culture and observation system, we found that rat mesenchymal stem cells (rMSCs) presented a contraction and re-spread (CRS) process when they were initially subjected to a physiological FSS (1.3 Pa). Our subsequent studies demonstrated that integrin and cilia played key roles in sensing FSS. Calcium, F-actin, and Rho-kinase were key molecules in the mechanotransduction of the CRS of the rMSCs. Our study revealed the immediate response of the rMSCs to FSS. It will be helpful for the understanding of MSC-related tissue repair and the role of MSCs in the initiation of atherosclerosis.
TL;DR: A method for replica molding electrospun fibers on the surface of polydimethylsiloxane (PDMS) is developed for culturing and guiding of cells, instead of ES fibers, to obtain microgrooves and microstructures composed of microgroove.
Abstract: A method for replica molding electrospun (ES) fibers on the surface of polydimethylsiloxane (PDMS) is developed for culturing and guiding of cells, instead of ES fibers. With this method, microgrooves and microstructures composed of microgrooves can be obtained. PDMS is integrated into the microfluidic chip as a substrate to successfully pattern and guide neurites on the PDMS surface with microgrooves.
TL;DR: An in vitro method for screening wound dressing candidates that can minimize the use of animals for developing better methods for wound care is demonstrated and a good correlation between in vitro and in vivo results is reported for fibrous wound dressings.
Abstract: This report demonstrates an in vitro method for screening wound dressing candidates that can minimize the use of animals for developing better methods for wound care. The development of materials and formulations for wound dressings, an important application of biomaterials, is laboriously and ethically challenging because of the use of a large number of animals. A method for rapid and effective screening of wound dressings in vitro, therefore, is in great need. A cell-on-a-chip model was used to simulate the cutaneous wound in vitro and screen the performances of several electrospun fibrous wound dressings in enhancing wound healing. For comparison, the performances of wound dressings were also evaluated in a rat model. It was found that the results acquired by microchip model corroborates well with animal experiments. It is the first time, as far as we know, that a good correlation between in vitro and in vivo results is reported for fibrous wound dressings. The cell-on-a-chip wound model we developed here may change the way that scientists screen candidates for wound dressings.
TL;DR: An in vitro model to simulate the microenvironment of endometriosis using microfluidic channels with cover slips to pattern and release endometrial stromal cells (ESCs) and human peritoneal mesothelial cells (HPMCs) in a way that mimicked the pathophysiology ofPeritoneal endometRIosis implicates that the peritoneAL physiology may play an important role in endometiosis.
Abstract: This paper demonstrates an in vitro model to simulate the microenvironment of endometriosis. We used microfluidic channels with cover slips to pattern and release endometrial stromal cells (ESCs) and human peritoneal mesothelial cells (HPMCs) in a way that mimicked the pathophysiology of peritoneal endometriosis. This approach enabled observation in real time interactions between ESCs and HPMCs both in their normal and pathological states. HPMCs from control individuals were able to resist the invasion of ESCs from both control and endometriotic individuals. By contrast, HPMCs from endometriotic individuals were unable to resist the invasion of ESCs from both normal and endometriotic individuals. We further analyzed the dynamics between HPMCs and ESCs from endometriotic individuals. HPMCs from endometriotic individuals relaxed their adhesion to each other at the beginning of invasion of ESCs, lose their adhesion to the substrate and apoptosed when surrounded by ESCs. These data implicate that the peritoneal physiology may play an important role in endometriosis.
TL;DR: A direct assay of IgG demonstrated that VAMI could simultaneously achieve higher sensitivity and require less time compared with conventional microfluidic immunoassays, and carry out a 3-step competitive assay for detecting the illegal food additive Sudan Red.
Abstract: This paper describes a vacuum-accelerated microfluidic immunoassay (we abbreviate it as VAMI) by sandwiching a filter membrane between a two-layer chip. A direct assay of IgG demonstrated that VAMI could simultaneously achieve higher sensitivity and require less time compared with conventional microfluidic immunoassays. We further applied VAMI to carry out a 3-step competitive assay (including antigen immobilization, competitive reaction and 2nd antibody reaction) for detecting the illegal food additive Sudan Red. A total assay time of 15 min with a limit of detection (LOD) of 1 ng ml-1 is achieved.
TL;DR: A rapid HIV assay combining screening and confirmation test by using the microfluidic network assay, which improved the assay speed while keeping the LOD of conventional ELISA and made it an excellent candidate for a quick HIV test for both screening
Abstract: The essential step for HIV spreading limitation is the screening tests. However, there are multiple disadvantages in current screening assays which need further confirmation test. Herein we developed a rapid HIV assay combining screening and confirmation test by using the microfluidic network assay. Meanwhile, the assay is accelerated by bypassing the step of blocking. We call this method as microfluidic assay without blocking (MAWB). Both the limit of detection and reagent incubation time of MAWB are determined by screening of one model protein pair: ovalbumin and its antibody. The assay time is accelerated about 25% while the limit of detection (LOD) is well kept. Formatting the method in for both HIV screening (testing 8 HIV-related samples) and confirmation (assaying 6 kinds of HIV antibodies of each sample) within 30 min was successful. Fast HIV screening and confirmation of 20 plasma samples were also demonstrated by this method. MAWB improved the assay speed while keeping the LOD of conventional ELISA. Meanwhile, both the accuracy and throughput of MAWB were well improved, which made it an excellent candidate for a quick HIV test for both screening and confirmation. Methods like this one will find wide applications in clinical diagnosis and biochemical analysis based on the interactions between pairs of molecules.
TL;DR: Programming-based image processing through the local recognition of a sub-array followed by the region-growing algorithm to achieve fast, convenient and precise extraction of information with reduced personal bias is presented.
Abstract: High-throughput assays necessitate high-throughput data analysis. Arrayed microfluidic immunoassay shows the capability of high-throughput protein detection. However, its development was restricted by the low efficiency of downstream data analysis. We present herein programming-based image processing through the local recognition of a sub-array followed by the region-growing algorithm to achieve fast, convenient and precise extraction of information with reduced personal bias.
TL;DR: In this article, a thiol-functionalized mesoporous silica nanorods (MSNRs) were synthesized through a base co-condensation method, in which two organoalkoxysilanes, tetraethoxylsilane (TEOS) and bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), were used as silica precursors simultaneously.
Abstract: Novel thiol-functionalized mesoporous silica nanorods (MSNRs) were synthesized through a base co-condensation method, in which two organoalkoxysilanes, tetraethoxylsilane (TEOS) and bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), were used as silica precursors simultaneously. TESPT was firstly used for both morphology control and inner surface functionalization of mesoporous silica hybrid materials. The microstructures as well as porous character of the MSNRs were characterized by means of SEM, XRD, TEM and N2 sorption measurements. Infrared spectrum analysis and heavy metal ions (Ag+ and Cd2+) adsorption measurements were carried out to confirm the functionalized framework of MSNRs.
TL;DR: In this article, a microfluidic chip for colorimetric Cu2+ detection based on gold nanoparticles was developed, which has a dynamic detection range from 0.75 to 50 µmol/L with only 20 µL solution including detection reagents and sample.
Abstract: We have developed a microfluidic chip for colorimetric Cu2+ detection. In this chip, it is facile to do colorimetric Cu2+ detection based on gold nanoparticles. This method has a dynamic detection range from 0.75 to 50 µmol/L with only 20 µL solution including detection reagents and sample. The result can be readout by naked eye and photographed by digital cameras. With the help of image processing software, we could measure the RGB value and calculate the Blue/Red ratio for more accurate quantification. Tap water could be detected in this portable chip.
TL;DR: This review focuses on currently available microscale methods that can control mammalian cells to assemble into 3D tissue-like structures.
Abstract: Different cell types make up tissues and organs hierarchically and communicate within a complex, three-dimensional (3D) environment. The in vitro recapitulation of tissue-like structures is meaningful, not only for fundamental cell biology research, but also for tissue engineering (TE). Currently, TE research adopts either the top-down or bottom-up approach. The top-down approach involves defining the macroscopic tissue features using biomaterial scaffolds and seeding cells into these scaffolds. Conversely, the bottom-up approach aims at crafting small tissue building blocks with precision-engineered structural and functional microscale features, using physical and/or chemical approaches. The bottom-up strategy takes advantage of the repeating structural and functional units that facilitate cell-cell interactions and cultures multiple cells together as a functional unit of tissue. In this review, we focus on currently available microscale methods that can control mammalian cells to assemble into 3D tissue-like structures.
Patent•
24 Oct 2012
TL;DR: In this paper, a method for acquiring a micro-nano structure by using high-voltage electrospinning die overturning on a material surface is presented, where the morphology of the groove is complimentary to that of the spinning.
Abstract: The invention provides a method for acquiring a micro-nano structure by using high-voltage electrospinning die overturning on a material surface. The method comprises the following steps: using high pressure static spinning as a template, adhering the spinning on an adhesive tape for fixing, then using a liquid prepolymer of a thermosetting polymer for die overturning, removing the thermosetted adhesive tape, thus generating grooves with corresponding patterns on the surface of the solidified polymer surface through the spinning, wherein the size is equal to that of the spinning, the morphology of the groove is complimentary to that of the spinning, the morphology can be uses as a nanofluidic pipeline for nanofluidic operation, and the growth of nerve cells can be induced and the surface hydrophobic performance of the polymer can be provided.
17 Dec 2012
TL;DR: The surface plasma resonance and surface-enhanced Raman scattering of gold nanoparticles are usually used to investigate the interaction between nanoparticles and proteins as mentioned in this paper, and factors such as the size and surface chemistry, property of proteins and environment of the solution can influence these interactions.
Abstract: Gold nanoparticles and proteins can interact via physical adsorption, chemically covalent conjugation, affinity adsorption and so on. The surface plasma resonance and surface-enhanced Raman scattering of gold nanoparticles are usually used to investigate the interaction between nanoparticles and protein. Factors such as the size and surface chemistry of gold nanoparticles, property of proteins and environment of the solution can influence these interactions. Gold nanoparticles are widely applied in the fields of highly effective and low-cost detections for disease and environmental pollutants, and play an important role in the disease therapy via the special physic-chemical properties of gold nanoparticles and the interactions between nanoparticles and proteins.