Douglas Goh

Highly sensitive SERS detection and quantification of sialic acid on single cell using photonic-crystal fiber with gold nanoparticles

An ultrasensitive surface enhanced Raman spectroscopy (SERS) based sensing platform was developed to detect the mean sialic acid level on the surface of single cell with sensitivity as low as 2 fmol. This platform adopted the use of an interference-free Raman tag, 4-(dihydroxyborophenyl) acetylene (DBA), which selectively binds to sialic acid on the cell membrane. By loading the side channel of a photonic crystal fiber with a mixture of gold nanoparticles and DBA-tagged HeLa cell, and subsequently propagating laser light through the central solid core, strong SERS signal was obtained. This SERS technique achieved accurate detection and quantification of concentration of sialic acid on a single cell, surpassing previously reported methods that required more than 10(5) cells. Moreover, this platform can be developed into a clinical diagnostic tool to potentially analyze sialic acid-related diseases such as tumor malignancy and metastasis in real-time.

A rapid and label-free SERS detection method for biomarkers in clinical biofluids.

A metal carbonyl-functionalized nanostructured substrate can be used in a rapid and simple assay for the detection of A1AT, a potential biomarker for bladder cancer, in clinical urine samples. The assay involves monitoring changes in the carbonyl stretching vibrations of the metal carbonyl via surface-enhanced Raman spectroscopy (SERS). These vibrations lie in the absorption spectral window of 1800-2200 cm(-1), which is free of any spectral interference from biomolecules.

In vitro toxicity and bioimaging studies of gold nanorods formulations coated with biofunctional thiol-PEG molecules and Pluronic block copolymers

Summary In this work, we investigated the cytotoxicity, colloidal stability and optical property of gold nanorods before and after functionalizing them with thiolated PEG and Pluronic triblock copolymer (PEO–PPO–PEO) molecules. The morphology of functionalized gold nanorods was characterized by UV–visible absorption spectroscopy, transmission electron microscopy, and dynamic light scattering. Solution phase synthesis of gold nanorods has remained the method of choice for obtaining varying shapes and aspect ratios of rod nanoparticles. This method typically involves the use of cetyltrimethylammonium bromide (CTAB) surfactants as directing agents to grow gold nanorods in the solution phase. The as-synthesized gold nanorods surfaces are terminated with CTAB molecules and this formulation gives rise to adverse toxicity in vitro and in vivo. To employ the gold nanorods for biological studies, it is important to eliminate or minimize the exposure of CTAB molecules from the gold nanorods surface to the local environment such as cells or tissues. Complete removal of CTAB molecules from the gold nanorods surface is unfeasible as this will render the gold nanorods structurally unstable, causing the aggregation of particles. Here, we investigate the individual use of thiolated PEG and PEO–PPO–PEO as capping agents to reduce the cytotoxicity of gold nanorods formulation, while maintaining the optical, colloidal, and structural properties of gold nanorods. We found that encapsulating gold nanorods with the thiolated PEG or PEO–PPO–PEO molecules guarantees the stability and biocompatibility of the nanoformulation. However, excessive use of these molecules during the passivation process leads to a reduction in the overall cell viability. We also demonstrate the use of the functionalized gold nanorods as scattering probes for dark-field imaging of cancer cells thereby demonstrating their biocompatibility. Our results offer a unique solution for the future development of safe scattering color probes for clinical applications such as the long term imaging of cells and tissues.

Pluronic Triblock Copolymer Encapsulated Gold Nanorods as Biocompatible Localized Plasmon Resonance-Enhanced Scattering Probes for Dark-Field Imaging of Cancer Cells

Gold nanorods (GNR) are synthesized using cetylmethylammonium bromide (CTAB) surfactants which function as structure-directing agents. However, CTAB forms a tightly bound cationic bilayer on GNR surface with the cationic trimethylammonium head group exposed to the aqueous media, which is known to be highly toxic in vitro and in vivo. Pluronic is a non-ionic triblock polymer, which can associate with CTAB and form stable CTAB–polymer complexes due to hydrophobic interactions. In this work, two types of Pluronic triblock copolymers were used to encapsulate GNR to reduce their cytotoxicity and improve colloidal and optical stability for biological applications. These formulations were characterized by UV–vis absorption spectra analysis, transmission electron microscopy, cell viability studies, differential interference contrast microscopy and dark-field imaging.

Sensitive surface enhanced Raman scattering multiplexed detection of matrix metalloproteinase 2 and 7 cancer markers

A surface enhanced Raman spectroscopy (SERS) based platform was developed for sensitive multiplexed detection of matrix metalloproteinases (MMP) (MMP-2 and MMP-7) with low limit of detection and high specificity. Detection is based on the virtue of enzymatic reaction where a peptide can be cleaved only by its corresponding enzyme. The platform comprises two components, a specialized SERS-based bimetallic-film-over-nanosphere (BMFON) substrate and gold nanoparticles (AuNPs). The two components were functionalized such that binding between the two would occur through biotin-avidin-biotin complexation. Binding is hindered by MMP peptide chains conjugated onto the surfaces of the substrate and AuNPs, and can be removed only by cleaving the peptide chains with corresponding enzymes. Since AuNP binding sites become free after the peptides are cleaved, the number of binding sites for AuNPs onto the substrate would increase. By tagging the AuNPs, concentrations of MMP-specific enzymes can be quantified through examining intensities of signature SERS peaks of the tags. This cleave-and-bind mechanism was first validated by individual detection and quantification of MMP-2 and MMP-7. The platform was demonstrated to be able to sensitively detect concentrations of specific enzymes ranging from 1 ng/mL to 40 µg/mL, with close correlation between SERS intensity and concentrations. Finally, the multiplexed detection of MMP-2 and MMP-7 was demonstrated. The multiplexity of this platform provides a robust way to analyze diseases associated with MMP-2 and MMP-7 enzymes. Our work can be further developed as a clinical diagnostic tool to detect other MMP proteinase in bio-fluids samples, widening the number of biomarkers needed to characterize diseases better.

Rapid SERS monitoring of lipid‐peroxidation‐derived protein modifications in cells using photonic crystal fiber sensor

We proposed a side channel photonic crystal fiber (SC-PCF) based Surface enhanced Raman spectroscopy (SERS) platform which is able to accurately monitor lipid peroxidation derived protein modifications in cells. This platform incorporates linoleamide alkyne (LAA), which is oxidized and subsequently modifies proteins in cells with alkyne functional group upon lipid peroxidation. By loading the side channel of SC-PCF with a mixture of gold nanoparticles and LAA treated cells, and subsequently measuring the interference-free alkyne Raman peak from these proteins in cells, strong SERS signal was obtained. The platform provides a method for the rapid monitoring of lipid peroxidation derived protein modification in cells.

High nuclearity carbonyl clusters as near-IR contrast agents for photoacoustic in vivo imaging

High nuclearity carbonyl clusters of ruthenium and osmium are found to exhibit good photoacoustic (PA) activity in the near-IR (NIR) region. Their potential as PA contrast agents for full body imaging has been demonstrated for the first time with mice; intravenous administration of the osmium carbonyl cluster Na2[Os10(μ6-C)(CO)24] afforded up to a four-fold enhancement of the PA signal in various tissues. The cluster exhibits low toxicity, high stability and superior PA stability compared to the clinically approved NIR dye, indocyanine green.

Novel Biodegradable Polymer Tethered Platinum (II) for Photoacoustic Imaging

Photoacoustic microscopy (PAM) is an emerging imaging diagnostic technique for various diseases. Coupled with contrast agents, photoacoustic (PA) imaging yields additional information to facilitate an accurate diagnosis. While many organic-based contrast agents, notably those of cyanine dyes, nanoparticles, polyhydroxy-fullerene and carbon nanotubes, have become available, the use of transition metal as contrast agent is scant. Here, for the first time, we report a platinum II-based biodegradable polymer for PA imaging that is capable of effective cellular internalization with very low cytotoxicity. The experiment results show great promise as a novel photoacoustic contrast agent as its detectable PA signal was observed both in cell imaging and in vivo rat cerebral vascular imaging via designed PAM. This work exemplifies the incorporation of transition metal complex with polymeric nanoparticles, further expanding the field of the ability of PA imaging.

Dual Trigger Crosslinked Micelles Based Polyamidoamine for Effective Paclitaxel Delivery

Targeted delivery of drugs in therapeutic applications is gaining traction in treating various diseases. However, its practicality is challenged by uncontrolled drug release. We present here a novel dual-trigger polyamidoaminebased crosslinked micelle vector that releases therapeutic drugs in response to triggers. The degradation of micelles can be controlled by redox and MMP-2 enzymatic activities. Such a system can achieve greater specificity for drug release than most recently reported micelle systems. Cytotoxicity tests of the micelles showed that they posed significantly lower toxicity towards normal cells as normal cells have relatively lower concentration of MMP-2 enzyme to disintegrate the micelles. The paclitaxel-conjugated micelles were effective in inducing apoptosis and cell cycle arrest in MDA-MB-231 cancer cells. The results demonstrated that the degradation of polyamidoamines could be fine-tuned by an enzyme-active peptide, thus increasing the anti-tumour efficacy and pave the way for development of highly controllable targeted drug delivery platforms.

Biomedicine with Surface Enhanced Raman Scattering (SERS)

Recently SERS is progressed as a sensitive biosensing modality due to the ‘fingerprint’ Raman spectra from analyte molecules. We present our recent achievements in sensitive biomarker sensing using SERS in a chip and fiber based platforms.