Zhuyuan Wang

SERS-Fluorescence Joint Spectral Encoding Using Organic–Metal–QD Hybrid Nanoparticles with a Huge Encoding Capacity for High-Throughput Biodetection: Putting Theory into Practice

A new concept of optical encoding approach, surface enhanced Raman scattering (SERS)-fluorescence joint spectral encoding method (SFJSE), was demonstrated by using organic-metal-quantum dot (QD) hybrid nanoparticles (OMQ NPs) with a nanolayered structure. This method has two distinct characteristics, which make it more feasible to achieve enormous codes in practice, compared with a sole fluorescence- or SERS-based encoding protocol. One of the two characteristics is to use the joint SERS and fluorescence spectra as the encoding elements instead of an individual optical signal, resulting in a broadened optical spectrum range for efficient encoding. The other is to assemble SERS reporters and fluorescent agents onto different layers of OMQ NPs, leading to an easier fabrication protocol when a large number of agents need to be involved into encoding carriers. By conjugating different antibodies to OMQ NPs with varied codes, the potential application of such an encoding system in high-throughput detection has been investigated by multiplex sandwich immunoassays. The high specificity and sensitivity of the assays suggest that the SFJSE method could be developed as a powerful encoding tool for high-throughput bioanalysis with the use of OMQ NPs.

Highly sensitive immunoassay based on Raman reporter-labeled immuno-Au aggregates and SERS-active immune substrate

A highly sensitive immunoassay based on surface enhanced Raman scattering (SERS) has been developed with a novel immune marker named as Raman reporter-labeled immuno-Au aggregates on a SERS-active immune substrate. The features of those immune aggregates were characterized by UV-vis extinction spectra, TEM images, SEM pictures and SERS spectra. It is found that stable gold aggregates in appropriate morphologies can be induced by mixing proper amounts of reporter molecules with gold nanoparticles. Based on those reporter-labeled Au aggregates, the immune aggregates with high stability can be prepared successfully by immobilizing antibody to the surface of the aggregates. Using those easily prepared aggregates showing strong SERS activity and high bio-specificity, a highly effective SERS-based immunoassay has been performed. Moreover, a SERS-active immune substrate has been introduced to replace a typical immune substrate without any SERS activity. Our experimental results indicate that the SERS-active immune substrate makes a certain contribution to the highly sensitive immunoassay. As a result, with this proposed immunoassay structure, the concentration detection of human-IgG was performed and a calibration curve was obtained in the range from 100ngmL(-1) to 100fgmL(-1). This work opens a new avenue for sensitive immunoassay and other biochemical analysis based on SERS.

Intracellular pH sensing using p-aminothiophenol functionalized gold nanorods with low cytotoxicity.

We report an intracellular pH sensor based on surface enhanced Raman scattering (SERS) using the hydrochloric acid (HCl) treated gold nanorods (GNRs) as the SERS substrates and p-aminothiophenol (pATP) as the Raman reporter. Using the HCl treated GNRs previously reported by us, the biocompatibility and the SERS performance of GNRs have been greatly improved. Meanwhile, the adsorbed reporters are allowed to be directly exposed to the surrounding environments, which is very important for biosensors. It is found that the SERS spectrum of pATP is strongly dependent on the pH value. The intensities of SERS bands at 1142 cm(-1), 1390 cm(-1), and 1432 cm(-1) increased obviously with the pH value varying from 3.0 to 8.0. This pH-dependent SERS performance of pATP-functionalized HCl treated GNRs was well retained after the incorporation of the GNRs into living HeLa cells. Our experimental results indicate that such pATP-functionalized HCl treated GNRs can be used as an effective intracellular pH sensor. Thus, we show a good example that the bioapplications of the normal CTAB-stabilized GNRs can be expanded after the simple HCl treatment.

pH and thermo dual-stimuli-responsive drug carrier based on mesoporous silica nanoparticles encapsulated in a copolymer-lipid bilayer.

A pH and thermo dual-controllable composite structure was developed as a triggerable drug delivery carrier. In such a drug carrier, a mesoporous silica nanoparticle (MSN) acts as the drug loading core, while a layer of copolymer-lipid serves as the dual-responsive gating shell. Specifically, the copolymer-lipid bilayer consists of natural phospholipids (soy phosphatidylcholine, SPC) and the poly(N-isopropylacrylamide-methacrylic acid-octadecyl acrylate) (p(NIPAM-MAA-ODA)) copolymer. With this structure, a high drug loading capacity and a sustained release effect could be provided by the MSN core, while a pH and thermo dual-responsive releasing ability could be offered by the copolymer-lipid bilayer. In addition, the introduction of SPC instead of the traditionally used phospholipids (such as dioleoyl phosphatidylethanolamine (DOPE) or dipalmitoyl phosphatidylcholine (DPPC)) results in a much lower cost and a better serum stability. Using doxorubicin (DOX) as the drug model, our results confirmed that either pH or temperature can trigger the drug release. However, much more drugs could be released by simultaneously controlling the pH and temperature. Furthermore, after being cocultured with cancer cells (MCF-7), the drug carriers transported DOX into the cells and exhibited a pH-sensitive release behavior. Since most tumor sites usually exhibit a more acidic environment or a higher temperature, the pH- and thermo-responsive releasing ability of this drug carrier is particularly useful and important for the targeted release at the tumor region. Thus, due to the powerful controlled releasing ability, the straightforward preparation method, and low cost, the demonstrated nanocarrier will have potential applications in controllable drug delivery and cancer therapy.

Dual-mode probe based on mesoporous silica coated gold nanorods for targeting cancer cells.

A dual-mode imaging probe for targeting cancer cells has been fabricated based on mesoporous silica coated gold nanorods (MS-GNRs) for the first time. In this probe, fluorescence and surface enhanced Raman scattering (SERS) signals can be generated independently by using different excitation wavelengths. To investigate the targeting performance of the probe, folic acid (FA) is conjugated on the outer surfaces of MS-GNRs as a targeting ligand and HeLa cells were used as model cancer cells because they overexpress folate receptors (FRs). The endocytosis mechanism was verified by competing experiments with free FA through both fluorescence images and SERS mappings. Moreover, the cytotoxicity of the probe was remarkably reduced in comparison with the GNRs without the silica shell as proved by the results of MTT assay. Compared with traditional imaging probes, this new type of nanoprobe has great potential for multiplexed imaging in living cells, which can be easily realized by using fluorescence and SERS signals.

A SERS-based immunoassay with highly increased sensitivity using gold/silver core-shell nanorods

An immunoassay based on surface enhanced Raman scattering (SERS) has been developed using immuno-gold/silver core-shell nanorods with a high sensitivity. The features of these nanoparticles were characterized by UV-vis extinction spectra, TEM images, EDX analyses and SERS spectra. It was found that the obtained gold/silver core-shell nanorods showed a much higher SERS activity than uncoated gold nanorods. After the gold/silver core-shell nanorods were modified with antibody and employed in immunoassay, the antigen concentration-dependent SERS spectra and dose-response calibration curves were obtained. By comparison, it can be concluded that the detection limit of gold/silver core-shell nanorods based immunoassay reaches 70 fM, which is 10(4) times lower than gold nanorods based detection. As a result, SERS probes fabricated with gold/silver core-shell nanorods are demonstrated to be advantageous to those synthesized with gold nanorods due to their highly increased sensitivity in sandwich immunoassay, which also indicates the potential use of these gold/silver core-shell nanorods in other biological sensing applications.

SERS Detection and Removal of Mercury(II)/Silver(I) using Oligonucleotide-Functionalized Core/Shell Magnetic Silica Sphere@Au Nanoparticles

Heavy metal ions, such as Hg(2+) and Ag(+), pose severe risks in human health and the environment. For sensitive detection and selective removal of Hg(2+) and Ag(+) ions, here, we demonstrate a surface-enhanced Raman scattering (SERS)-active platform by employing the oligonucleotide-functionalized magnetic silica sphere (MSS)@Au nanoparticles (NPs). This system exploits mismatched T-Hg-T and C-Ag-C bridges to capture Hg(2+) and Ag(+) ions, exhibiting excellent responses for Hg(2+) ions in the range of 0.1-1000 nM and for Ag(+) in the range of 10-1000 nM. The assay is highly selective for the target ions and does not respond to other metal ions. Additionally, the Hg(2+) and Ag(+) ions in this system can be effectively removed from surrounding solutions by an external magnetic field or through spontaneous precipitation. Moreover, more than 80% of the MSS@Au NPs can be easily recycled with the help of cysteine. We anticipate that the designed strategy could be extended to other analytes that can bind to DNA molecules with a high affinity, and can be used in many potential applications such as environmental renovation, toxin detection, and groundwater analysis.

A SERS and fluorescence dual mode cancer cell targeting probe based on silica coated Au@Ag core–shell nanorods

We report a dual mode cancer cell targeting probe based on CdTe quantum dots (QDs) conjugated, silica coated Au@Ag core-shell nanorods (Au@Ag NRs), which can generate both surface enhanced Raman scattering (SERS) and fluorescence signals. In such a probe, folic acid (FA) is used as a targeting ligand for folate receptors (FRs) overexpressed cancer cells. To synthesize the probe, Au@Ag NRs were first prepared to serve as the SERS substrates by coating an Ag shell on the gold nanorods. Then the Au@Ag NRs were labeled with 4-mercaptobenzoic acid (4MBA) to generate SERS signals, followed by being coated with a silica shell through a modified Stöber method. Finally, CdTe QDs and FA were conjugated to the silica coated Au@Ag NRs by the carbodiimide chemistry to yield fluorescence and the targeting ability, respectively. To validate the targeting capability of the probe, in vitro experiments were conducted, using HeLa cells with overexpressed FRs as the model target cells and MRC-5 cells with a low folate receptor expression level as the negative control. Both the fluorescence imaging and the SERS mapping results confirmed that the proposed probe can be used as an efficient cancer cell targeting agent. This kind of multifunctional probe has great potential in the diagnosis and therapeutics of cancerous diseases due to its specific targeting and multiplex imaging abilities, especially in the simultaneous tracking of multiple components in a hybrid bio-system.

Distinguishing breast cancer cells using surface-enhanced Raman scattering

AbstractThe detection and identification of epidermal growth factor receptor 2 (HER2)-positive breast cancer cells is crucial for the clinic therapy of breast cancer. For the aim of the detection, a novel surface-enhanced Raman scattering (SERS) probe for distinguishing breast cancers at different HER2 statuses is reported in this paper. In such a probe, anti-HER2 antibody-conjugated silver nanoparticles have been synthesized for specific targeting of HER2-positive breast cancer cells. More importantly, different from the previously reported SERS probe for targeting cancer cells, p-mercaptobenzoic acid is utilized as both the Raman reporter and the conjugation agent for attaching antibody molecules, which leads to a much simplified structure. For investigating the ability of such a probe to distinguish breast cancer cells, SKBR3 and MCF7 cells were chosen as two model systems, which are HER2-positive- and HER2-negative-expressing cells, respectively. The experimental results reveal that SKBR3 cells exhibit much stronger SERS signals than MCF7 cells, indicating that the probe could be utilized to distinguish breast cancer cells at different HER2 statuses. This kind of SERS probe holds a potential for a direct detection of living breast cancer cells with the advantages of easy fabrication, high SERS sensitivity, and biocompatibility. FigureSERS spectra of the probe in SKBR3 cells and in MCF7 cells

Rapid and reproducible analysis of thiocyanate in real human serum and saliva using a droplet SERS-microfluidic chip

As thiocyanate (SCN(-)) acts as an important biomarker in human health assessment, there remains an urgent need to realize rapid and reproducible analysis of SCN(-) in body fluids. Here, a droplet microfluidic device has been designed and fabricated for SCN(-) detection in real human serum and saliva using the surface enhanced Raman scattering (SERS) technique. Only a few minutes are needed for the whole detection process which simply cost a few microliters of real sample. Gold@silver core-shell nanorods (Au@Ag NRs) with a large SERS enhancement factor were selected to capture SCN(-) ions in body fluids. The intensity of SERS peak at around 2100 cm(-1), which originates from the -C≡N stretching mode, was used to indicate the concentrations of SCN(-) ions. Importantly, by generating a droplet environment for mixing reagents and acquiring signals, this microfluidic platform possesses the advantages of an improved reproducibility and reduced time consumption. For practical applications, the SERS-microfluidic system is capable to achieve rapid analysis of SCN(-) in the presence of human serum, which is very important for realizing the detection in real biological samples. Additionally, SCN(-) in saliva samples was detected in the SERS-microfluidic chip and the results provide useful information for distinguishing between smokers and nonsmokers.