Guangyu Qiu

Direct detection of two different tumor-derived extracellular vesicles by SAM-AuNIs LSPR biosensor

Extracellular vesicles (EVs) are abundant in various biological fluids including blood, saliva, urine, as well as extracellular milieu. Accumulating evidence has indicated that EVs, which contain functional proteins and small RNAs, facilitate intercellular communication between neighbouring cells, and are critical to maintain various physiological processes. In contrast, EV-derived toxic signals can spread out over the tissues adjacent to the injured area in certain diseases, including brain tumors and neurodegenerative disorders. This demands better characterization of EVs which can be employed for liquid biopsy clinically as well as for the study of intercellular signalling. Exosomes and microvesicles share a number of similar characteristics, but it is important to distinguish between these two types of EVs. Here, we report for the first time that our in-house developed Localized Surface Plasmon Resonance biosensor with self-assembly gold nanoislands (SAM-AuNIs) can be used to detect and distinguish exosomes from MVs isolated from A-549 cells, SH-SY5Y cells, blood serum, and urine from a lung cancer mouse model. Exosomes, compared with MVs, produced a distinguishable response to the bare LSPR biosensor without functionalization, suggesting a different biophysical interaction between exosomes and MVs with SAM AuNIs. This sensor attains the limit of detection to 0.194µg/ml, and the linear dynamic range covers 0.194-100µg/ml. This discovery not only reveals great insight into the distinctive membrane property of tumor-derived exosomes and MVs, but also facilitate the development of novel LSPR biosensors for direct detection and isolation of heterogeneous EVs.

Label-free detection of 3-nitro-l-tyrosine with nickel-doped graphene localized surface plasmon resonance biosensor

3-nitro-l-tyrosine (3-NT) is believed to be a biomarker of neurodegenerative diseases and metal doped graphene possess exceptionally high binding energy of 3-NT with metal-nitro chemisorption. Here we report a novel label-free detection scheme of 3-NT via nickel-doped graphene (NDG) as the functionalized receptor on our phase detecting localized surface plasmon resonance (LSPR) biosensor. When compared with reported 3-NT immunoassay with enzyme-linked immunosorbent assay (ELISA), our NDG-LSPR platform offers two advantages i.e. 1) label-free and 2) capture of 3-NT by direct chemisorption. Our limit of detection for 3-NT in PBS was found to be 0.13pg/ml and the linear dynamic range of response was from 0.5pg/ml to 1ng/ml, i.e. four orders of magnitude. The specificity of our NDG receptor to 3-NT was also verified with l-tyrosine of equivalent concentrations in PBS and diluted human serum, for which the NDG receptor shows negligible responses. In addition, the adsorption of 3-NT and l-tyrosine to the NDG receptor were also investigated by atomic force microscopy and further verified by surface enhanced Raman spectroscopy. Therefore, our NDG-LSPR biosensor competes favorably against ELISA and we believe it should be an attractive and economical solution to early diagnostic of 3-NT related disorders for clinical applications.

Differential phase-detecting localized surface plasmon resonance sensor with self-assembly gold nano-islands.

Self-assembly (SAM) gold nano-islands are fabricated by two-step thin-film deposition-annealing method. Despite random distribution of the SAM, the p-polarized light after total internal reflection shows significant phase transition at the extinction wavelengths upon refractive index variation due to localized surface plasmon resonance (LSPR) effect. It resembles the sharp phase transition observed in conventional surface plasmon resonance (SPR) biosensors, so that the bulk sensitivity of the SAM-LSPR sensor is improved via the phase interrogation method. In this Letter, we present both computational and experimental investigations to the SAM-LSPR sensor and the results show excellent agreement with each other. With bulk refractive index resolution to 9.75×10(-8)  RIU, we believe the phase-detecting SAM-LSPR sensor would be an essential step toward low-cost label-free sensing applications.

Label-Free LSPR Detection of Trace Lead(II) Ions in Drinking Water by Synthetic Poly(mPD-co-ASA) Nanoparticles on Gold Nanoislands

Using self-assembly gold nanoislands (SAM-AuNIs) functionalized by poly(m-phenylenediamine-co-aniline-2-sulfonic acid) (poly(mPD-co-ASA)) copolymer nanoparticles as specific receptors, a highly sensitive localized surface plasmon resonance (LSPR) optochemical sensor is demonstrated for detection of trace lead cation (Pb(II)) in drinking water. The copolymer receptor is optimized in three aspects: (1) mole ratio of mPD:ASA monomers, (2) size of copolymer nanoparticles, and (3) surface density of the copolymer. It is shown that the 95:5 (mPD:ASA mole ratio) copolymer with size less than 100 nm exhibits the best Pb(II)-sensing performance, and the 200 times diluted standard copolymer solution contributes to the most effective functionalization protocol. The resulting poly(mPD-co-ASA)-functionalized LSPR sensor attains the detection limit to 0.011 ppb toward Pb(II) in drinking water, and the linear dynamic range covers 0.011 to 5000 ppb (i.e., 6 orders of magnitude). In addition, the sensing system exhibits robust selectivity to Pb(II) in the presence of other metallic cations as well as common anions. The proposed functional copolymer functionalized on AuNIs is found to provide excellent Pb(II)-sensing performance using simple LSPR instrumentation for rapid drinking-water inspection.

Label-free surface plasmon resonance biosensing with titanium nitride thin film

In this report, titanium nitride thin film synthesized with reactive magneto-sputtering technique is proposed as an alternative surface plasmon resonance sensing material. The physical and chemical natures were initially studied by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. In virtue of white-light common-path sensing system, the wavelength modulated TiN films achieved tunable evanescent plasmonic field from 573 nm to 627 nm. The optimized TiN film with 29.8 nm thickness exhibited good differential phase sensitivity (i.e. 1.932 × 10-7 RIU) to refractive index alteration, which is comparable to the performance of gold film. We have also attained direct measurement of biotin adsorption on the TiN and monitored sub-sequential biotin-streptavidin conjugation. It was found that TiN films have significantly higher binding affinity toward biotin than that of gold in experiments, so we are able to detect biotin directly to 0.22 µg/ml (0.90 µM) in label-free manner. The adsorption mechanism of biotin on TiN(200) are also explored with periodic density functional theory (DFT) via computer simulation and it was found that the exceptional biotin-TiN affinity may be due to the stacking formation of both N-Ti and O-Ti bonds. Also, the adsorption energy of biotin-TiN was found to be - 1.85 eV, which was two times higher than that of biotin-gold. Both experimental and computational results indicate, for the first time, that the TiN film can be directly functionalized with biotin molecules, thus it serves as an alternative plasmonic material to existing gold-based SPR biosensors.

Transport in polymer-supported chemically-doped CVD graphene

In this study we report on the electron transport in flexible-transparent polymer supported chemically doped chemical vapour deposited (CVD) graphene. We investigate the modified carrier transport following doping with various metal chlorides. An increase in the work function was noted for AuCl3-, FeCl3-, IrCl3-, and RhCl3-doping, whilst only SnCl2 doping showed a reduced work function. We attribute this to dopant-mediated charge transfer resulting in the formation of neutral atomic species. The neutral and near-neutral atomic populations produced metallic aggregates, with this agglomeration level critically dependent on the cohesive energy of the metallic component in each dopant. Micron-scale spatial conductivity mapping highlighted the spatially uniform low resistance of AuCl3-doped graphene. Local conductivity enhancements at grain boundaries and lattice defects within the as-synthesised polycrystalline graphene suggested that the dopant molecules tend to reside at lattice imperfections. Temperature dependent transport studies indicated that the shifted work function improved electrical conductivity due to the increase of barrier transparency between grain boundaries. Variable Range Hopping (VRH) dominated at temperatures <140 K in undoped graphene, whereas combined Nearest Neighbour Hopping (NNH) and diffusive transport appears to play a major role throughout the transport in all doped samples. The findings herein reveal that the underlying extended transport mechanisms associated with chemically doped CVD graphene transferred to polymer supports contrast with the highly localised transport in undoped graphene.