Amino-acid- and peptide-directed synthesis of chiral plasmonic gold nanoparticles.

Understanding chirality, or handedness, in molecules is important because of the enantioselectivity that is observed in many biochemical reactions 1 , and because of the recent development of chiral metamaterials with exceptional light-manipulating capabilities, such as polarization control2-4, a negative refractive index 5 and chiral sensing 6 . Chiral nanostructures have been produced using nanofabrication techniques such as lithography 7 and molecular self-assembly8-11, but large-scale and simple fabrication methods for three-dimensional chiral structures remain a challenge. In this regard, chirality transfer represents a simpler and more efficient method for controlling chiral morphology12-18. Although a few studies18,19 have described the transfer of molecular chirality into micrometre-sized helical ceramic crystals, this technique has yet to be implemented for metal nanoparticles with sizes of hundreds of nanometres. Here we develop a strategy for synthesizing chiral gold nanoparticles that involves using amino acids and peptides to control the optical activity, handedness and chiral plasmonic resonance of the nanoparticles. The key requirement for achieving such chiral structures is the formation of high-Miller-index surfaces ({hkl}, h ≠ k ≠ l ≠ 0) that are intrinsically chiral, owing to the presence of 'kink' sites20-22 in the nanoparticles during growth. The presence of chiral components at the inorganic surface of the nanoparticles and in the amino acids and peptides results in enantioselective interactions at the interface between these elements; these interactions lead to asymmetric evolution of the nanoparticles and the formation of helicoid morphologies that consist of highly twisted chiral elements. The gold nanoparticles that we grow display strong chiral plasmonic optical activity (a dis-symmetry factor of 0.2), even when dispersed randomly in solution; this observation is supported by theoretical calculations and direct visualizations of macroscopic colour transformations. We anticipate that our strategy will aid in the rational design and fabrication of three-dimensional chiral nanostructures for use in plasmonic metamaterial applications.

Plasmon-enabled degradation of organic micropollutants in water by visible-light illumination of Janus gold nanorods.

The development of sustainable methods for the degradation of pollutants in water is an ongoing critical challenge. Anthropogenic organic micropollutants such as pharmaceuticals, present in our water supplies in trace quantities, are currently not remediated by conventional treatment processes. Here, we report an initial demonstration of the oxidative degradation of organic micropollutants using specially designed nanoparticles and visible-wavelength sunlight. Gold "Janus" nanorods (Au JNRs), partially coated with silica to enhance their colloidal stability in aqueous solutions while also maintaining a partially uncoated Au surface to facilitate photocatalysis, were synthesized. Au JNRs were dispersed in an aqueous solution containing peroxydisulfate (PDS), where oxidative degradation of both simulant and actual organic micropollutants was observed. Photothermal heating, light-induced hot electron-driven charge transfer, and direct electron shuttling under dark conditions all contribute to the observed oxidation chemistry. This work not only provides an ideal platform for studying plasmonic photochemistry in aqueous medium but also opens the door for nanoengineered, solar-based methods to remediate recalcitrant micropollutants in water supplies.

Gold nanoshell-localized photothermal ablation of prostate tumors in a clinical pilot device study.

Biocompatible gold nanoparticles designed to absorb light at wavelengths of high tissue transparency have been of particular interest for biomedical applications. The ability of such nanoparticles to convert absorbed near-infrared light to heat and induce highly localized hyperthermia has been shown to be highly effective for photothermal cancer therapy, resulting in cell death and tumor remission in a multitude of preclinical animal models. Here we report the initial results of a clinical trial in which laser-excited gold-silica nanoshells (GSNs) were used in combination with magnetic resonance-ultrasound fusion imaging to focally ablate low-intermediate-grade tumors within the prostate. The overall goal is to provide highly localized regional control of prostate cancer that also results in greatly reduced patient morbidity and improved functional outcomes. This pilot device study reports feasibility and safety data from 16 cases of patients diagnosed with low- or intermediate-risk localized prostate cancer. After GSN infusion and high-precision laser ablation, patients underwent multiparametric MRI of the prostate at 48 to 72 h, followed by postprocedure mpMRI/ultrasound targeted fusion biopsies at 3 and 12 mo, as well as a standard 12-core systematic biopsy at 12 mo. GSN-mediated focal laser ablation was successfully achieved in 94% (15/16) of patients, with no significant difference in International Prostate Symptom Score or Sexual Health Inventory for Men observed after treatment. This treatment protocol appears to be feasible and safe in men with low- or intermediate-risk localized prostate cancer without serious complications or deleterious changes in genitourinary function.

Polyaniline@Au organic-inorganic nanohybrids with thermometer readout for photothermal immunoassay of tumor marker.

A photothermal immunoassay using a thermometer as readout based on polyaniline@Au organic-inorganic nanohybrids was built. Temperature output is acquired due to the photothermal effect of the photothermal nanomaterial. Polyaniline@Au organic-inorganic nanohybrids were synthesized by interfacial reactions with high photothermal conversion efficiency. A sandwich structure of the immunocomplex was prepared on a microplate for determination of carcinoembryonic antigen (CEA) by polyaniline@Au organic-inorganic nanohybrids as nanolabel. The released heat based on light-to-heat conversion from the photothermal nanolabel under NIR irradiation is detectable using the thermometer. The increased temperature is directly proportional to CEA concentration. The linear range of the photothermal immunoassay is 0.20 to 25 ng mL-1 with determination limit of 0.17 ng mL-1. Polyaniline@Au organic-inorganic nanohybrids with high photothermal conversion efficiency was synthesized as labels to construct photothermal immunosensor. The sandwich-type immunoassay was built on 96 hole plate based on specific binding of antigen and antibody. Carcinoembryonic antigen in sample was detected quantitatively by thermometer readout.

Fluorescent detection of microRNA-21 in MCF-7 cells based on multifunctional gold nanorods and the integration of chemotherapy and phototherapy.

MicroRNA-21 is an important biomarker of tumor early prediction and metastasis, and its accurate detection is of great significance for tumor diagnosis and treatment. It will be a meaningful work to combine the detection of RNA with chemotherapy and photothermal therapy on the same composite material. Herein, we designed a multifunctional nanocomposite based on gold nanorods (AuNRs), making use of microRNA-triggered drug release and near-infrared photothermal effect, which has been developed for cancer therapy and microRNA-21detection. Firstly, the AuNRs with photothermal effect were synthesized as carriers for drug delivery. Then the surface of gold nanorods was modified by functional DNA chains to provide an efficient site for doxorubicin (DOX) loading. Finally, folic acid was introduced to achieve the targeted treatment of MCF-7 cells. The microRNA competed with the double-stranded DNA, resulting in the release of DOX and the recovery of fluorescence signal located at 595 nm with an excitation of 488 nm effectively. The nano-biosensor could not only achieve dual-function of diagnosis and treatment of cancer cells, but also accomplish the detection of microRNA in tumor cells. It showed a high selectivity for microRNA-21 determination with a limit of detection (LOD) of 2.1 nM from the linear relationship from 1.0 × 10-5 M to 5.0 × 10-7 M. This scheme provides an outstanding strategy for cell imaging, treatment, and detection, which serves as a promising candidate in the field of biomedical research.

Thermophoretic Detection of Exosomal microRNAs by Nanoflares.

Exosomal microRNAs (miRNAs) are reliable and noninvasive biomarkers for the early diagnosis of cancer. Yet, accurate and feasible detection of exosomal miRNAs is often hampered by the low abundance of miRNAs in exosomes and the requirement for RNA extraction in large sample volumes. Here we show a thermophoretic sensor implemented with nanoflares for in situ detection of exosomal miRNAs, without resorting to either RNA extraction or target amplification. Thermophoretic accumulation of nanoflare-treated exosomes leads to an amplified fluorescence signal upon the binding of exosomal miRNAs to nanoflares, allowing for direct and quantitative measurement of exosomal miRNAs down to 0.36 fM in 0.5 µL serum samples. One of the best markers, exosomal miR-375, showed an accuracy of 85% for detection of estrogen receptor-positive breast cancer at early stages (stages I, II). This work provides a feasible tool to improve the diagnosis of cancer.

Real-Time Imaging Redox Status in Biothiols and Ferric Metabolism of Cancer Cells in Ferroptosis Based on Switched Fluorescence Response of Gold Carbon Dots.

Ferroptosis is an iron-dependent form of regulated cell death. In this study, a ratiometric fluorescent probe, gold carbon dots (GCDs) consisting of carbon skeleton and gold nanoclusters, was used for in situ imaging to monitor redox status in biothiols (glutathione and cysteine) and ferric metabolism of cancer cells in ferroptosis. The as-prepared GCDs can selectively respond to biothiols, interestingly, the fluorescence may be switched to sense ferric ions without interference by biothiols under proper conditions. The robust GCDs-probe exhibits excellent photobleaching resistance and can reversibly respond to intracellular biothiols/ferric ion with high temporal resolution. The 8 h real-time imaging of living cells was employed to track the fluctuation of biothiols, showing the change of redox status in ferroptosis. In addition, release of ferric ions in cells was monitored. The real-time imaging of depletion of biothiols and release of ferric ion in cells indicates the GCDs-probe can monitor how the ferroptosis regulates redox status in biothiols and ferric metabolism.

Virus-Sized Gold Nanorods: Plasmonic Particles for Biology.

Plasmons, collective oscillations of conduction-band electrons in nanoscale metals, are well-known phenomena in colloidal gold and silver nanocrystals that produce brilliant visible colors in these materials that depend on the nanocrystal size and shape. Under illumination at or near the plasmon bands, gold and silver nanocrystals exhibit properties that enable fascinating biological applications: (i) the nanocrystals elastically scatter light, providing a straightforward way to image them in complex aqueous environments; (ii) the nanocrystals produce local electric fields that enable various surface-enhanced spectroscopies for sensing, molecular diagnostics, and boosting of bound fluorophore performance; (iii) the nanocrystals produce heat, which can lead to chemical transformations at or near the nanocrystal surface and can photothermally destroy nearby cells. While all the above-mentioned applications have already been well-demonstrated in the literature, this Account focuses on several other aspects of these nanomaterials, in particular gold nanorods that are approximately the size of viruses (diameters of ∼10 nm, lengths up to 100 nm). Absolute extinction, scattering, and absorption properties are compared for gold nanorods of various absolute dimensions, and references for how to synthesize gold nanorods with four different absolute dimensions are provided. Surface chemistry strategies for coating nanocrystals with smooth or rough shells are detailed; specific examples include mesoporous silica and metal-organic framework shells for porous (rough) coatings and polyelectrolyte layer-by-layer wrapping for "smooth" shells. For self-assembled-monolayer molecular coating ligands, the smoothest shells of all, a wide range of ligand densities have been reported from many experiments, yielding values from less than 1 to nearly 10 molecules/nm2 depending on the nanocrystal size and the nature of the ligand. Systematic studies of ligand density for one particular ligand with a bulky headgroup are highlighted, showing that the highest ligand density occurs for the smallest nanocrystals, even though these ligand headgroups are the most mobile as judged by NMR relaxation studies. Biomolecular coronas form around spherical and rod-shaped nanocrystals upon immersion into biological fluids; these proteins and lipids can be quantified, and their degree of adsorption depends on the nanocrystal surface chemistry as well as the biophysical characteristics of the adsorbing biomolecule. Photothermal adsorption and desorption of proteins on nanocrystals depend on the enthalpy of protein-nanocrystal surface interactions, leading to light-triggered alteration in protein concentrations near the nanocrystals. At the cellular scale, gold nanocrystals exert genetic changes at the mRNA level, with a variety of likely mechanisms that include alteration of local biomolecular concentration gradients, changes in mechanical properties of the extracellular matrix, and physical interruption of key cellular processes-even without plasmonic effects. Microbiomes, both organismal and environmental, are the likely first point of contact of nanomaterials with natural living systems; we see a major scientific frontier in understanding, predicting, and controlling microbe-nanocrystal interactions, which may be augmented by plasmonic effects.

Fluorescence turn-off-on for highly selective detection of serum l-cysteine based on AuNCs-AuNPs ensembles.

The discriminative monitoring of biothiols in biological fluids is a great challenge. Herein, we developed a fluorescence "turn-off-on" probe based on AuNCs-AuNPs ensembles, which detected l-cysteine (l-Cys) with high selectivity. The strong blue fluorescence of l-hydroxyproline-capped gold nanoclusters (l-Hyp@AuNCs) at 465 nm was quenched by AuNPs via the inner filter effect. Interestingly, the fluorescence was recovered by interaction with l-Cys due to the electrostatic and specific Au-S interactions between l-Cys and AuNPs. The effect of the l-Cys amount on the fluorescence "off-on" efficiency showed good linearity in the range of 1.5-35.0 µM (R2 = 0.986) with a detection limit of 1.4 µM (3σ). The proposed method was successfully applied to test the serum l-Cys levels without the interference of glutathione, homocysteine and methionine. The AuNCs-AuNPs ensembles-based fluorescence "turn-off-on" protocol shows great potential in specific biothiol sensing.

A novel turn-on fluorescent sensor for the sensitive detection of glutathione via gold nanocluster preparation based on controllable ligand-induced etching.

In this study, we report a facile one-pot chemical etching approach to simply and rapidly prepare gold nanoclusters capped with luminol (Lum-AuNCs) in an alkaline aqueous solution at room temperature. A series of characterization studies have been carried out to explore the morphology, the optical properties and chemical components of Lum-AuNCs. The average diameter of Lum-AuNCs is 1.8 ± 0.3 nm, exhibiting fluorescence near 510 nm upon excitation at 420 nm with a quantum yield of 14.29% and an average fluorescence lifetime of 9.47 ns. On the basis of the ligand-induced etching of glutathione (GSH) to the intermediate (luminol capped gold nanoparticles, abbreviated as Lum-AuNPs), a novel and simple method for the fluorescence determination of GSH has been established. The method displays a good linear response in the range of 0.05-300 µM toward GSH with a limit of detection of 35 nM. This detection strategy with high sensitivity and selectivity facilitates its practical application for the detection of GSH levels in cell extracts. The in vitro cell results illustrate that Lum-AuNCs have good cytocompatibility and can be used to readily differentiate normal cells and tumor cells.

Kinetics of molecular decomposition under irradiation of gold nanoparticles with nanosecond laser pulses-A 5-Bromouracil case study.

Laser illuminated gold nanoparticles (AuNPs) efficiently absorb light and heat up the surrounding medium, leading to versatile applications ranging from plasmonic catalysis to cancer photothermal therapy. Therefore, an in-depth understanding of the thermal, optical, and electron induced reaction pathways is required. Here, the electrophilic DNA nucleobase analog 5-Bromouracil (BrU) has been used as a model compound to study its decomposition in the vicinity of AuNPs illuminated with intense ns laser pulses under various conditions. The plasmonic response of the AuNPs and the concentration of BrU and resulting photoproducts have been tracked by ultraviolet and visible (UV-Vis) spectroscopy as a function of the irradiation time. A kinetic model has been developed to determine the reaction rates of two parallel fragmentation pathways of BrU, and their dependency on laser fluence and adsorption on the AuNP have been evaluated. In addition, the size and the electric field enhancement of the decomposed AuNPs have been determined by atomic force microscopy and finite domain time difference calculations, respectively. A minor influence of the direct photoreaction and a strong effect of the heating of the AuNPs have been revealed. However, due to the size reduction of the irradiated AuNPs, a trade-off between laser fluence and plasmonic response of the AuNPs has been observed. Hence, the decomposition of the AuNPs might be limiting the achievable temperatures under irradiation with several laser pulses. These findings need to be considered for an efficient design of catalytic plasmonic systems.

Photoinduced charge transfer in Zn(II) and Au(III)-ligated symmetric and asymmetric bacteriochlorin dyads: A computational study.

The excited-state properties and photoinduced charge-transfer (CT) kinetics in a series of symmetrical and asymmetrical Zn- and Au-ligated meso-meso-connected bacteriochlorin (BChl) complexes are studied computationally. BChl derivatives, which are excellent near-IR absorbing chromophores, are found to play a central role in bacterial photosynthetic reaction centers but are rarely used in artificial solar energy harvesting systems. The optical properties of chemically linked BChl complexes can be tuned by varying the linking group and involving different ligated metal ions. We investigate charge transfer in BChl dyads that are either directly linked or through a phenylene ring (1,4-phenylene) and which are ligating Zn or Au ions. The directly linked dyads with a nearly perpendicular arrangement of the BChl units bear markedly different properties than phenylene linked dyads. In addition, we find that the dielectric dependence of the intramolecular CT rate is very strong in neutral Zn-ligated dyads, whereas cationic Au-ligated dyads show negligible dielectric dependence of the CT rate. Rate constants of the photo induced CT process are calculated at the semiclassical Marcus level and are compared to fully quantum mechanical Fermi's golden rule based values. The rates are calculated using a screened range separated hybrid functional that offers a consistent framework for addressing environment polarization. We study solvated systems in two solvents of a low and a high scalar dielectric constant.

Photocatalytically renewable peptide-based electrochemical impedance method for sensing lipopolysaccharide.

A peptide (Li5-025)-modified gold nanoparticle (AuNP)/(titania (TiO2) + 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphine (TAPP))/glassy carbon electrode (GCE) was developed for lipopolysaccharide (LPS) determination. This electrode not only performs well in the electrochemical impedance determination of LPS in serum but can also be easily regenerated under light irradiation. Using Fe(CN)63-/4- as a redox probe, LPS recognition can be indicated by the significantly increased electron-transfer resistance (Ret) as a result of the coaction of the increased steric hindrance from the peptide-LPS complex and the electrostatic repulsion between LPS and Fe(CN)63-/4-. The impedimetric signal was acquired in the frequency range 0.1 Hz ~ 100 kHz with an initial voltage of 174 mV and an amplitude of 10 mV. The resistance changes (ΔRet) are linearly related to the LPS concentrations in a broad range (0.1 pg mL-1 ~ 100 ng mL-1) with a low detection limit (0.08 pg mL-1). Importantly, the electrode shows high selectivity to LPS from Escherichia coli O55:B5 compared to other bacterial sources and considerable anti-interference to 0.1% fetal calf serum, demonstrating its potential application in clinically relevant samples. Another highlight is that the AuNP/(TiO2 + TAPP)/GCE surface can be photocatalytically regenerated under light irradiation (50 mW cm-2, 300-2500 nm) without any obvious damage to the electrode microstructure. After simple peptide re-immobilization, the regenerated electrode demonstrates LPS response similar to the peptide less one, and the deviation is only 2.89% after 5-cycle reuse. Graphical abstract A peptide (Li5-025)-modified AuNP/(TiO2 + TAPP porphine)/GCE was proposed, which not only has excellent electrochemical analytical performances for LPS assay in serum but also can be reused after light irradiation and subsequent peptide re-immobilization.

Mechanism of Photoredox-Initiated C-C and C-N Bond Formation by Arylation of IPrAu(I)-CF3 and IPrAu(I)-Succinimide.

Herein, we report on the photoredox-initiated gold-mediated C(sp2)-CF3 and C(sp2)-N coupling reactions. By adopting gold as a platform for probing metallaphotoredox catalysis, we demonstrate that cationic gold(III) complexes are the key intermediates of the C-C and C-N coupling reactions. The high-valent gold(III) intermediates are accessed by virtue of photoredox catalysis through a radical chain process. In addition, the bond-forming step of the coupling reactions is the reductive elimination from cationic gold(III) intermediates, which is supported by isolation and crystallographic characterization of key Au(III) intermediates.

Bulk/Surface Defects Engineered TiO2 Nanotube Photonic Crystals Coupled with Plasmonic Gold Nanoparticles for Effective in Vivo Near-Infrared Light Photoelectrochemical Detection.

Photoelectrochemical (PEC) techniques are of fundamental and practical importance, and they have been widely used for solar energy conversion and experimental protection. Besides these important applications, an emerging and fast developing PEC application of PEC bioanalysis is receiving more attention from both academic and clinic communities. However, the typical PEC biosensing is still limited under illumination of ultraviolet and visible (UV/vis) light, which hampers its in vivo detection in deep tissues. Expanding the optical absorption wavelength of photoelectrodes from the UV/vis light region into the near-infrared (NIR) light region is highly desirable due to its deep tissue penetrability and minimal invasiveness for organisms, but the exploration of a facile strategy to implement efficient NIR absorption with biocompatible materials is still a big challenge. Herein, under the guidance of theorical calculations, we propose a strategy through modulation of bulk/surface defects and decoration of Au nanoparticles on TiO2 nanotube photonic crystals to implement efficient NIR response and thus successfully realize sensitive and selective PEC detection of antibiotics in real bio- and experimental-samples under NIR illumination. In addition, we first implement the in vivo PEC detection under illumination of NIR light. We have faith that this new NIR photoelectric responsive strategy will provide a broad platform for detection of life-related biomolecules in deep tissues or even in vivo for real-time measurement and shed light on the intrinsic connections between biomarkers and clinical diseases.

Palindromic Molecular Beacon Based Z-Scheme BiOCl-Au-CdS Photoelectrochemical Biodetection.

This work presented an innovative and rationally engineered palindromic molecular beacon (PMB) based "Z-scheme" photoelectrochemical (PEC) biosensing protocol for the selective screening of kanamycin (Kana) through DNA hybridization-induced conformational conversion. Interestingly, the ingeniously designed PMB integrated the multifunctional elements including recognition region, primer-like palindromic fragment, and polymerization-nicking template. The cosensitized structures consisted of CdS quantum dot functionalized hairpin DNA2 (QD-HP2) and region-selectively deposited gold nanoparticles onto {001} facets of bismuth oxychloride (BiOCl-Au). Compared with BiOCl-Au alone, the attachment of CdS QDs onto BiOCl-Au (i.e., BiOCl-Au-CdS QDs) exhibited evidently enhanced photocurrent intensity thanks to the synergistic effect of Z-scheme BiOCl-Au-CdS QDs. After incubation with target Kana, Kana-aptamer binding could induce the exposure of PMB region for hairpin DNA1 (HP1). The exposed palindromic tails hybridized with each other (like a molecular machine) to consume the substrates (dNTPs) and fuels (enzyme) for the releasing of numerous nick fragments (Nick). The as-generated nick fragments could specifically hybridize with the complementary region of QD-HP2, thus resulting in decreasing photocurrent because of the increasing spatial distance for electron transfer between two-type photosensitizers. Under optimum conditions, the PMB-based sensing system exhibited satisfying photocurrent responses toward target Kana within the working range from 50 to 5000 fM at a low detection limit of 29 fM. Impressively, the concept of a palindromic fragment-mediated primer-free biosensing strategy offers a new avenue for advanced development of efficient and convenient biodetection systems.

On-chip plasmonic immunoassay based on targeted assembly of gold nanoplasmonic particles.

Developing a sensitive and selective detection platform of disease-related biomarkers is important for the diagnosis and treatment of diseases at an early stage. Among clinically meaningful biomarkers, proteins are the most commonly used indicators, and they are generally detected via immunoassays. However, the use of conventional immunoassays in early diagnosis is hindered by the time required, complex steps, high-cost, and insufficient sensitivity and selectivity. Herein, we developed a novel on-chip immunoassay with degassing-driven microfluidic devices and gold nanoplasmonic particles (GNPs). To recognize target proteins, antibody-conjugated GNPs as probes were used in the assay owing to their excellent scattering properties. Using the proposed nonenzymatic immunoassay, we detected amyloid ß (Aß) and Tau proteins, representative biomarkers of Alzheimer's disease, in femtomolar levels. Selective and quantitative detection of Aß spiked in blood plasma was also achieved for further clinical application of the proposed immunoassay. The proposed plasmonic immunoassay integrated with degassing-driven microfluidic chips provides a new platform for biological assays and diagnosis.

Photocurrent enhancement by a local electric field on DNA-modified electrodes covered with gold nanoparticles.

We here describe a photocurrent generation system exploiting gold nanoparticles (AuNPs) that cover perylenediimide-DNA complexes on electrode surfaces. Enhanced photocurrents were generated by the irradiation of the AuNPs, attributed to the efficient excitation of the perylenediimides by a local electric field on the surface of the AuNPs.

A synchrotron-based infrared microspectroscopy study on the cellular response induced by gold nanoparticles combined with X-ray irradiations on F98 and U87-MG glioma cell lines.

The inclusion of nanoparticles (NP) in radiotherapy has been shown to increase the damaging effect on tumor cells. However, the mechanisms of action of NP combined with radiotherapy, and the influence of NP parameters and cell type on their radiosensitization capability at molecular and cellular levels still remain unclear. Gold NP (AuNP) have become particularly popular due to their multiple advantages. Within this context, our research work aimed to study the biochemical radiosensitization capacity of F98 and U87-MG glioma cell lines to 1.9 nm AuNP combined with X-ray irradiation. For this purpose, synchrotron-based infrared microspectroscopy (SR-FTIRM) was used as a powerful tool for biochemical composition and treatment response assessment of cells at a single-cell level. SR-FTIRM data, supported by multivariate analysis, revealed clear AuNP-induced changes in the DNA, protein and lipid spectral regions. The AuNP-related biochemical alterations appear prior to the irradiation, which gave us a first indication on the AuNP radiosensitization action. Biochemical modifications induced by the AuNP in the presence of radiotherapy irradiations include enhanced conformational changes in the protein secondary structures, variations in the intensity and position in the phosphodiester bands, and changes in the CH2 and CH3 stretching modes. These changes are better manifested at 24 hours post-irradiation time. SR-FTIRM results showed a clear heterogeneity in the biochemical cell response, probably due to the distinct cell-NP interactions and thus, to different DNA damage and cell death processes.

A surface plasmon resonance enhanced photoelectrochemical immunoassay based on perovskite metal oxide@gold nanoparticle heterostructures.

An innovative visible light-driven photoelectrochemical (PEC) immunosensing system was reasonably established for the sensitive detection of prostate-specific antigen (PSA) by using perovskite metal oxide@gold nanoparticle heterostructures (BaTiO3/Au) as the photoactive materials. When plasmonic Au nanoparticles were directly decorated on BaTiO3, a several times surface plasmon resonance (SPR) enhancement of photocurrent density was induced via the injection of hot electrons from visible light-excited Au nanoparticles into the conduction band of BaTiO3, and the combination of BaTiO3 and Au nanoparticles was employed as a promising platform for developing a photoelectrochemical bioanalysis. As a proof of concept, PSA had been detected by the BaTiO3/Au nanocomposite-based PEC sensor. To design such an immunoassay protocol, a monoclonal anti-PSA capture antibody (cAb)-coated microplate and glucose oxidase/polyclonal anti-PSA detection antibody-modified gold nanoparticles (GOx-Au NP-dAb) were used as the immunoreaction platform and signal probe, respectively. Upon the addition of target PSA, a sandwiched immunocomplex was formed accompanying the immuno-recognition between the antigen and antibody, and then the carried GOx could oxidize glucose to produce H2O2. The photocurrent of the BaTiO3/Au nanocomposite-functionalized electrode amplified with increasing H2O2 concentration since H2O2 is considered as a good hole scavenger. On the basis of the above-mentioned mechanisms and the optimized conditions, the assembled PEC immunosensor was linear with the logarithm of the PSA concentration in the range of 0.01-40 ng mL-1 with a detection limit of 4.2 pg mL-1. It afforded rapid response, good precision, and high stability and specificity, implying its great promise in photoelectrochemical immunoassays. More generally, this system sets up an ideal PEC immunosensing system based on the BaTiO3/Au nanocomposites and represents an innovative and low-cost "signal-on" assay scheme for the practical quantitative screening of low-abundance proteins.