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.

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.

Common-path spectral interferometry with temporal carrier for highly sensitive surface plasmon resonance sensing.

Incorporating the temporal carrier technique with common-path spectral interferometry, we have successfully demonstrated an advanced surface plasmon resonance (SPR) biosensing system which achieves refractive index resolution (RIR) up to 2 × 10(-8) refractive index unit (RIU) over a wide dynamic range of 3 × 10(-2) RIU. While this is accomplished by optimizing the SPR differential phase sensing conditions with just a layer of gold, we managed to address the spectral phase discontinuity with a novel spectral-temporal phase measurement scheme. As the new optical setup supersedes its Michelson counterpart in term of simplicity, we believe that it is a significant contribution for practical SPR sensing applications.

White-light spectral interferometry for surface plasmon resonance sensing applications.

A novel differential phase detecting surface plasmon resonance (SPR) sensor based on white-light spectral interferometry is presented. Our proposed scheme employs a white-light source for SPR excitation and measures the corresponding SPR phase change at the optimized coupling wavelength with fixed angle of incidence across the visible spectrum. Compared to existing laser based phase detecting schemes, this system offers optimal sensitivity and extended dynamic range of measurement without any compromise in phase detection resolution. Results obtained from sodium chloride solutions indicate that the detection limit is 2.6×10⁻7 RIU over a refractive index range of 10⁻² RIU, which is considerably wider than that achievable by existing laser based approach, thus making our scheme very attractive for practical SPR sensing applications.

In vivo liquid biopsy for glioblastoma malignancy by the AFM and LSPR based sensing of exosomal CD44 and CD133 in a mouse model.

Glioblastoma (GBM) is the fatal brain tumor in which secreted lactate enhances the expression of cluster of differentiation 44 (CD44) and the release of exosomes, cell-derived nanovesicles (30-200 nm), and therefore promotes tumor malignant progression. This study found that lactate-driven upregulated CD44 in malignant Glioblastoma cells (GMs) enhanced the release of CD44-enriched exosomes which increased GMs' migration and endothelial cells' tube formation, and CD44 in the secreted exosomes was sensitively detected by "capture and sensing" Titanium Nitride (TiN) - Nanoholes (NH) - discs immunocapture (TIC) - atomic force microscopy (AFM) and ultrasensitive TiN-NH-localized surface plasmon resonance (LSPR) biosensors. The limit of detection for exosomal CD44 with TIC-AFM- and TiN-NH-LSPR-biosensors was 5.29 × 10-1 µg/ml and 3.46 × 10-3 µg/ml in exosome concentration, respectively. Importantly, this work first found that label-free sensitive TiN-NH-LSPR biosensor could detect and quantify enhanced CD44 and CD133 levels in immunocaptured GMs-derived exosomes in the blood and the cerebrospinal fluid of a mouse model of GBM, supporting its potential application in a minimally invasive molecular diagnostic for GBM progression as liquid biopsy.

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.

Encapsulating Co2 P@C Core-Shell Nanoparticles in a Porous Carbon Sandwich as Dual-Doped Electrocatalyst for Hydrogen Evolution.

A highly efficient and pH-universal hydrogen evolution reaction (HER) electrocatalyst with a sandwich-architecture constructed using zero-dimensional N- and P-dual-doped core-shell Co2 P@C nanoparticles embedded into a 3 D porous carbon sandwich (Co2 P@N,P-C/CG) was synthesized through a facile two-step hydrothermal carbonization and pyrolysis method. The interfacial electron transfer rate and the number of active sites increased owing to the synergistic effect between the N,P-dual-doped Co2 P@C core-shell and sandwich-nanostructured substrates. The presence of a high surface area and large pore sizes improved the mass-transfer dynamics. This nanohybrid showed remarkable electrocatalytic activity toward the HER in a wide pH range with good stability. The computational study and experiments revealed that the carbon atoms close to the N and P dopants on the shell of Co2 P@N,P-C were effective active sites for HER catalysis and that both Co2 P and the N,P dopants gave rise to an optimized binding free energy of H on the active sites.

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.

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.

A redox-controlled electrolyte for plasmonic enhanced dye-sensitized solar cells.

Plasmonic enhanced dye-sensitized solar cells (DSSCs) with metallic nanostructures suffer from corrosion problems, especially with the presence of the iodine/triiodide redox couple in the electrolyte. Herein, we introduce an alternative approach by compensating the corrosion with a modified liquid electrolyte. In contrast to the existing method of surface preservation for plasmonic nanostructures, the redox-controlled electrolyte (RCE) contains iodoaurate intermediates, i.e. gold(i) diiodide (AuI2-) and gold(iii) tetraiodide (AuI4-) with optimal concentrations, such that these intermediates are readily reduced to gold nanoparticles during the operation of DSSCs. As corrosion and redeposition of gold occur simultaneously, it effectively provides corrosion compensation to the plasmonic gold nanostructures embedded in the photoanode. Cycling tests of the specific amount of gold contents in the RCE of DSSCs support the fact that the dissolution and deposition of gold are reversible and repeatable. This gold deposition on the TiO2 photoanode results in forming a Schottky barrier (SB) at the metal-semiconductor interface and effectively inhibits the recombination of electron-hole pairs. Therefore, the RCE increases the short-circuit current, amplifies the open-circuit voltage, and reduces the impedance of the TiO2/dye interface. The power conversion efficiency of DSSCs was improved by 57% after incorporating the RCE.

Initial Reduction of CO2 on Pd-, Ru-, and Cu-Doped CeO2(111) Surfaces: Effects of Surface Modification on Catalytic Activity and Selectivity.

Surface modification by metal doping is an effective treatment technique for improving surface properties for CO2 reduction. Herein, the effects of doped Pd, Ru, and Cu on the adsorption, activation, and reduction selectivity of CO2 on CeO2(111) were investigated by periodic density functional theory. The doped metals distorted the configuration of a perfect CeO2(111) by weakening the adjacent Ce-O bond strength, and Pd doping was beneficial for generating a highly active O vacancy. The analyses of adsorption energy, charge density difference, and density of states confirmed that the doped metals were conducive for enhancing CO2 adsorption, especially for Cu/CeO2(111). The initial reductive dissociation CO2 → CO* + O* on metal-doped CeO2(111) followed the sequence of Cu- > perfect > Pd- > Ru-doped CeO2(111); the reductive hydrogenation CO2 + H → COOH* followed the sequence of Cu- > perfect > Ru- > Pd-doped CeO2(111), in which the most competitive route on Cu/CeO2(111) was exothermic by 0.52 eV with an energy barrier of 0.16 eV; the reductive hydrogenation CO2 + H → HCOO* followed the sequence of Ru- > perfect > Pd-doped CeO2(111). Energy barrier decomposition analyses were performed to identify the governing factors of bond activation and scission along the initial CO2 reduction routes. Results of this study provided deep insights into the effect of surface modification on the initial reduction mechanisms of CO2 on metal-doped CeO2(111) surfaces.

Methanol Oxidation on Pt3Sn(111) for Direct Methanol Fuel Cells: Methanol Decomposition.

PtSn alloy, which is a potential material for use in direct methanol fuel cells, can efficiently promote methanol oxidation and alleviate the CO poisoning problem. Herein, methanol decomposition on Pt3Sn(111) was systematically investigated using periodic density functional theory and microkinetic modeling. The geometries and energies of all of the involved species were analyzed, and the decomposition network was mapped out to elaborate the reaction mechanisms. Our results indicated that methanol and formaldehyde were weakly adsorbed, and the other derivatives (CHxOHy, x = 1-3, y = 0-1) were strongly adsorbed and preferred decomposition rather than desorption on Pt3Sn(111). The competitive methanol decomposition started with the initial O-H bond scission followed by successive C-H bond scissions, (i.e., CH3OH → CH3O → CH2O → CHO → CO). The Brønsted-Evans-Polanyi relations and energy barrier decomposition analyses identified the C-H and O-H bond scissions as being more competitive than the C-O bond scission. Microkinetic modeling confirmed that the vast majority of the intermediates and products from methanol decomposition would escape from the Pt3Sn(111) surface at a relatively low temperature, and the coverage of the CO residue decreased with an increase in the temperature and decrease in partial methanol pressure.

Differential spectral phase interferometry for wide dynamic range surface plasmon resonance biosensing.

We introduce a novel wide dynamic range phase-sensitive surface plasmon resonance (SPR) biosensor based on differential spectral interferometry. Superseding conventional spectroscopic approach where only the SPR dip is monitored, our system acquires the spectral phase information of the entire electromagnetic field that undergoes SPR transformation. Since the SPR-induced phase change is highly wavelength specific with fixed incident angle, ultra-high sensitivity achievable through phase-sensitive detection, as reported herein, is maintained continuously across the spectral domain in response to refractive index changes. Our system has demonstrated a detection limit of 2.2×10(-7) in terms of refractive index unit (RIU) using standard single-layer gold surface. In terms of biosensing performance, the estimated detection sensitivity obtained from bovine serum albumin (BSA) antibody-antigen binding experiments is 0.5 ng ml(-1).