Highly sensitive detection of carbendazim in agricultural products using colorimetric and photothermal lateral flow immunoassay based on plasmonic gold nanostars.

The wide use and high toxicity of carbendazim (CBD) in agriculture pose unprecedented demands for convenient, sensitive, and cost-effective on-site monitoring. Herein, we propose a novel colorimetric and photothermal dual-mode lateral flow immunoassay (LFIA) based on plasmonic gold nanostars (AuNSs) for CBD detection in agricultural products. The AuNSs were synthesized via a rapid seed-mediated growth method (with growth time of ∼5 s). A stable immunoprobe was formed by adsorbing CBD antibodies onto AuNSs. This immunoprobe exhibited high conversion efficiency and sensitivity in photothermal detection with a low limit of detection (LOD) of 0.28 ng mL-1. The LOD of the colorimetric mode was higher (0.48 ng mL-1). The results of CBD detection in various agricultural products aligned well with ultra-performance liquid chromatography tandem mass spectrometry. Overall, our LFIA shows excellent sensitivity, specificity, reproducibility, and rapidness in CBD detection, and thus is a highly potential on-site platform in resource-limited environments.

Amino acid-induced synthesis of chiral AgAuPt nanoparticles with branched structure for circularly polarized enantioselective photoelectrocatalytic water splitting.

Chiral Plasmonic nanomaterials have gradually illustrated intriguing circularly polarized light (CPL)-dependent properties in photocatalysis due to their unique chiral optical activity. However, the connection between chiral characteristics and catalytic performance of these materials in cooperative systems is rarely reported and remains a challenge task. In this work, branched AgAuPt nanoparticles induced by L/d-cysteine (Cys) with strong and perfectly symmetric circular dichroism (CD) signals are synthesized. Chiral branched AgAuPt nanoparticles firstly exhibit superior typical electrocatalytic performance. In the photoelectrocatalytic system, chiral branched AgAuPt nanoparticles demonstrate selective catalytic water splitting performance. Specifically, chiral branched AgAuPt with related CPL irradiation exhibits enhanced acidic hydrogen evolution reaction (HER) performance. Under the continuous irradiation of related CPL, the chiral catalyst generates more heat, which further increases the catalytic activity. This contribution of heat is supported by density functional theory (DFT) calculation results. The changes in chiroptical activity during this process are recorded by variable temperature CD spectra. This work provides a novel paradigm for designing chiral catalysis systems and emphasizes the profound promise of chiral plasmonic nanomaterials as chiral catalysts.

Understanding the Behaviors of Plasmon-Induced Hot Carriers and Their Applications in Photocatalysis.

Photocatalysis driven by plasmon-induced hot carriers has been gaining increasing attention. Recent studies have demonstrated that plasmon-induced hot carriers can directly participate in photocatalytic reactions, leading to great enhancement in solar energy conversion efficiency, by improving the catalytic activity or changing selectivity. Nevertheless, the utilization efficiency of hot carriers remains unsatisfactory. Therefore, how to correctly understand the generation and transfer process of hot carriers, as well as accurately differentiate between the possible mechanisms, have become a key point of attention. In this review, we overview the fundamental processes and mechanisms underlying hot carrier generation and transport, followed by highlighting the importance of hot carrier monitoring methods and related photocatalytic reactions. Furthermore, possible strategies for the further characterization of plasmon-induced hot carriers and boosting their utilization efficiency have been proposed. We hope that a comprehensive understanding of the fundamental behaviors of hot carriers can aid in designing more efficient photocatalysts for plasmon-induced photocatalytic reactions.

Recent Advances in the 3D Chiral Plasmonic Nanomaterials.

From the view of geometry, chirality is that an object cannot overlap with its mirror image, which has been a fundamental scientific problem in biology and chemistry since the 19th century. Chiral inorganic nanomaterials serve as ideal templates for investigating chiral transfer and amplification mechanisms between molecule and bulk materials, garnering widespread attentions. The chiroptical property of chiral plasmonic nanomaterials is enhanced through localized surface plasmon resonance effects, which exhibits distinctive circular dichroism (CD) response across a wide wavelength range. Recently, 3D chiral plasmonic nanomaterials are becoming a focal research point due to their unique characteristics and planar-independence. This review provides an overview of recent progresses in 3D chiral plasmonic nanomaterials studies. It begins by discussing the mechanisms of plasmonic enhancement of molecular CD response, following by a detailed presentation of novel classifications of 3D chiral plasmonic nanomaterials. Finally, the applications of 3D chiral nanomaterials such as biology, sensing, chiral catalysis, photology, and other fields have been discussed and prospected. It is hoped that this review will contribute to the flourishing development of 3D chiral nanomaterials.

Plasmonic Cu2-xSe Mediated Colorimetric/Photothermal Dual-Readout Detection of Glutathione.

Plasmonic nanomaterials have attracted great attention in the field of catalysis and sensing for their outstanding electrical and optical properties. Here, a representative type of nonstoichiometric Cu2-xSe nanoparticles with typical near-infrared (NIR) localized surface plasma resonance (LSPR) properties originating from their copper deficiency was applied to catalyze the oxidation of colorless TMB into their blue product in the presence of H2O2, indicating they had good peroxidase-like activity. However, glutathione (GSH) inhibited the catalytic oxidation of TMB, as it can consume the reactive oxygen species. Meanwhile, it can induce the reduction of Cu(II) in Cu2-xSe, resulting in a decrease in the degree of copper deficiency, which can lead to a reduction in the LSPR. Therefore, the catalytic ability and photothermal responses of Cu2-xSe were decreased. Thus, in our work, a colorimetric/photothermal dual-readout array was developed for the detection of GSH. The linear calibration for GSH concentration was in the range of 1-50 µM with the LOD as 0.13 µM and 50-800 µM with the LOD as 39.27 µM. To evaluate the practicability of the assay, tomatoes and cucumbers were selected as real samples, and good recoveries indicated that the developed assay had great potential in real applications.

Second Near-Infrared Plasmonic Nanomaterials for Photoacoustic Imaging and Photothermal Therapy.

Photoacoustic imaging (PAI) and imaging-guided photothermal therapy (PTT) in the second near-infrared window (NIR-II, 1000-1700 nm) have received increasing attention owing to their advantages of greater penetration depth and higher signal-to-noise ratio. Plasmonic nanomaterials with tunable optical properties and strong light absorption provide an alternative to dye molecules, showing great prospects for phototheranostic applications. In this review, the research progress in principally modulating the optical properties of plasmonic nanomaterials, especially affecting parameters such as size, morphology, and surface chemical modification, is introduced. The commonly used plasmonic nanomaterials in the NIR-II window, including noble metals, semiconductors, and heterostructures, are then summarized. In addition, the biomedical applications of these NIR-II plasmonic nanomaterials for PAI and PTT in phototheranostics are highlighted. Finally, the perspectives and challenges for advancing plasmonic nanomaterials for practical use and clinical translation are discussed.

Ostensible Steady-State Molecular Cooling with Plasmonic Gold Nanoparticles.

The optical and chemical properties of plasmonic materials have sparked extensive research in exploring their applications in various areas such as photocatalysts, chemical sensors, and photonic devices. However, complicated plasmon-molecule interactions have posed substantial obstacles for the development of plasmonic material-based technologies. Quantifying plasmon-molecule energy transfer processes is a crucial step to understand the complex interplay between plasmonic materials and molecules. Here we report an anomalous steady-state reduction in the anti-Stokes to Stokes surface-enhanced Raman spectroscopy (SERS) scattering intensity ratio of aromatic thiols adsorbed on plasmonic gold nanoparticles under continuous-wave laser irradiation. The observed reduction of the scattering intensity ratio is closely related to the excitation wavelength, the surrounding media, and component of the plasmonic substrates used. Moreover, we observed a similar extent of scattering intensity ratio reduction with a range of aromatic thiols and under different external temperatures. Our discovery implies that there are either unexplained wavelength-dependent SERS outcoupling effects, or some unrecognized plasmon-molecule interactions which lead to a nanoscale plasmon refrigerator for molecules. This effect should be taken into consideration for the design of plasmonic catalysts and plasmonic photonic devices. Moreover, it could be useful for cooling large molecules under ambient conditions.

Environmentally Friendly Improvement of Plasmonic Nanostructure Functionality towards Magnetic Resonance Applications.

Plasmonic nanostructures have attracted a broad research interest due to their application perspectives in various fields such as biosensing, catalysis, photovoltaics, and biomedicine. Their synthesis by pulsed laser ablation in pure water enables eliminating various side effects originating from chemical contamination. Another advantage of pulsed laser ablation in liquids (PLAL) is the possibility to controllably produce plasmonic nanoparticles (NPs) in combination with other plasmonic or magnetic materials, thus enhancing their functionality. However, the PLAL technique is still challenging in respect of merging metallic and semiconductor specific features in nanosized objects that could significantly broaden application areas of plasmonic nanostructures. In this work, we performed synthesis of hybrid AuSi NPs with novel modalities by ultrashort laser ablation of bulk gold in water containing silicon NPs. The Au/Si atomic ratio in the nanohybrids was finely varied from 0.5 to 3.5 when changing the initial Si NPs concentration in water from 70 µg/mL to 10 µg/mL, respectively, without requiring any complex chemical procedures. It has been found that the laser-fluence-insensitive silicon content depends on the mass of nanohybrids. A high concentration of paramagnetic defects (2.2·× 1018 spin/g) in polycrystalline plasmonic NPs has been achieved. Our findings can open further prospects for plasmonic nanostructures as contrast agents in optical and magnetic resonance imaging techniques, biosensing, and cancer theranostics.

A Multilayered Mesoporous Gold Nanoarchitecture for Ultraeffective Near-Infrared Light-Controlled Chemo/Photothermal Therapy for Cancer Guided by SERS Imaging.

Surface-enhanced Raman scattering (SERS) imaging has emerged as a promising tool for guided cancer diagnosis and synergistic therapies, such as combined chemotherapy and photothermal therapy (chemo-PTT). Yet, existing therapeutic agents often suffer from low SERS sensitivity, insufficient photothermal conversion, or/and limited drug loading capacity. Herein, a multifunctional theragnostic nanoplatform consisting of mesoporous silica-coated gold nanostar with a cyclic Arg-Gly-Asp (RGD)-coated gold nanocluster shell (named RGD-pAS@AuNC) is reported that exhibits multiple "hot spots" for pronouncedly enhanced SERS signals and improved near-infrared (NIR)-induced photothermal conversion efficiency (85.5%), with a large capacity for high doxorubicin (DOX) loading efficiency (34.1%, named RGD/DOX-pAS@AuNC) and effective NIR-triggered DOX release. This nanoplatform shows excellent performance in xenograft tumor model of HeLa cell targeting, negligible cytotoxicity, and good stability both in vitro and in vivo. By SERS imaging, the optimal temporal distribution of injected RGD/DOX-pAS@AuNCs at the tumor site is identified for NIR-triggered local chemo-PTT toward the tumor, achieving ultraeffective therapy in tumor cells and tumor-bearing mouse model with 5 min of NIR irradiation (0.5 W cm-2 ). This work offers a promising approach to employing SERS imaging for effective noninvasive tumor treatment by on-site triggered chemo-PTT.

Photomagnetically Powered Spiky Nanomachines with Thermal Control of Viscosity for Enhanced Cancer Mechanotherapy.

Nanomachines with active propulsion have emerged as an intelligent platform for targeted cancer therapy. Achieving an efficient locomotion performance using an external energy conversion is a key requirement in the design of nanomachines. In this study, inspired by diverse spiky structures in nature, a photomagnetically powered nanomachine (PMN) with a spiky surface and thermally dependent viscosity tunability is proposed to facilitate mechanical motion in lysosomes for cancer mechanotherapy. The hybrid nanomachine is integrated with magnetic nanoparticles as the core and covered with gold nanotips. Physical simulations and experimental results prove that the spiky structure endows nanomachines with an obvious photomagnetic coupling effect in the NIR-II region through the alignment and orienting movement of plasmons on the gold tips. Using a coupling-enhanced magnetic field, PMNs are efficiently assembled into chain-like structures to further elevate energy conversion efficiency. Notably, PMNs with the thermal control of viscosity are efficiently propelled under simultaneously applied dual external energy sources in cell lysosomes. Enhanced mechanical destruction of cancer cells via PMNs is confirmed both in vitro and in vivo under photomagnetic treatment. This study provides a new direction for designing integrated nanomachines with active adaptability to physiological environments for cancer treatment.

Recent Development in Plasmonic Nanobiosensors for Viral DNA/RNA Biomarkers.

Recently, due to the coronavirus pandemic, the need for early diagnosis of infectious diseases, including viruses, is emerging. Though early diagnosis is essential to prevent infection and progression to severe illness, there are few technologies that accurately measure low concentrations of biomarkers. Plasmonic nanomaterials are attracting materials that can effectively amplify various signals, including fluorescence, Raman, and other optical and electromagnetic output. In this review, we introduce recently developed plasmonic nanobiosensors for measuring viral DNA/RNA as potential biomarkers of viral diseases. In addition, we discuss the future perspective of plasmonic nanobiosensors for DNA/RNA detection. This review is expected to help the early diagnosis and pathological interpretation of viruses and other diseases.

Surface plasmon resonance: A promising approach for label-free early cancer diagnosis.

Cancer is the second leading cause of death worldwide after cardiovascular disease. The major cause of high mortality is delayed detection. Therefore, detection at an early stage followed by early treatment can mitigate morbidity as well as mortality. The utilization of biomarker-based detection tools helps in early-stage recognition. Fortunately, biomarkers indicating disease status are released in to the circulation. These include traditional marker proteins as well as exosomes, micro-RNA (miRNA) and circulating tumor DNA (ct-DNA). Biosensors are biological and chemical reaction devices that generate signals based on analyte concentration. Due to analyte binding, these devices demonstrate high sensitivity and specificity. This review examines the use of surface plasmon resonance (SPR)-based sensors in the diagnosis of various cancer including those of the breast, prostate, lung, ovary, cervix and pancreas. SPR is a label-free, real-time and non-invasive optical biosensing technology representing a novel diagnostic tool in cancer detection.

A Novel 3D Hierarchical Plasmonic Functional Cu@Co3O4@Ag Array as Intelligent SERS Sensing Platform with Trace Droplet Rapid Detection Ability for Pesticide Residue Detection on Fruits and Vegetables.

Rapid and effective detection of pesticide residues from complex surfaces of fruits and vegetables has important significance. Herein, we report a novel three-dimensional (3D) hierarchical porous functional surface-enhanced Raman scattering (SERS) substrate, which is fabricated by successive two-step hydrothermal synthesis strategy of silver nanoparticles (Ag NPs) and cobalt oxide nanowires (Co3O4 NWs) on the 3D copper foam framework as Cu@Co3O4@Ag-H. The strategy offers a new avenue for localized plasmonic materials distribution and construction, which exhibits better morphology regulation ability and SERS activity (or hotspots engineering) than physical spurring obtained Cu@Co3O4@Ag-S. The developed Cu@Co3O4@Ag-H possesses large surface area and rich hotspots, which contributes to the excellent SERS performance, including homogeneity (RSD of 7.8%), sensitivity (enhancement factor, EF of 2.24 × 108) and stability. The Cu@Co3O4@Ag-H not only provides plenty of Electromagnetic enhancement (EM) hotspots but also the trace detection capability for droplet rapid sensing within 2 s. Cu@Co3O4@Ag-H substrate is further developed as an effective SERS sensing platform for pesticide residues detection on the surfaces of fruits and vegetables with excellent LOD of 0.1 ppm, which is lower than the most similar reported works. This work offers new potential for bioassay, disease POCT diagnosis, national security, wearable flexible devices, energy storage and other related fields.

Direct and Label-Free Monitoring of Albumin in 2D Fatty Liver Disease Model Using Plasmonic Nanogratings.

Non-alcoholic fatty liver (NAFLD) is a metabolic disorder related to a chronic lipid accumulation within the hepatocytes. This disease is the most common liver disorder worldwide, and it is estimated that it is present in up to 25% of the world's population. However, the real prevalence of this disease and the associated disorders is unknown mainly because reliable and applicable diagnostic tools are lacking. It is known that the level of albumin, a pleiotropic protein synthesized by hepatocytes, is correlated with the correct function of the liver. The development of a complementary tool that allows direct, sensitive, and label-free monitoring of albumin secretion in hepatocyte cell culture can provide insight into NAFLD's mechanism and drug action. With this aim, we have developed a simple integrated plasmonic biosensor based on gold nanogratings from periodic nanostructures present in commercial Blu-ray optical discs. This sensor allows the direct and label-free monitoring of albumin in a 2D fatty liver disease model under flow conditions using a highly-specific polyclonal antibody. This technology avoids both the amplification and blocking steps showing a limit of detection within pM range (≈0.26 ng/mL). Thanks to this technology, we identified the optimal fetal bovine serum (FBS) concentration to maximize the cells' lipid accumulation. Moreover, we discovered that the hepatocytes increased the amount of albumin secreted on the third day from the lipids challenge. These data demonstrate the ability of hepatocytes to respond to the lipid stimulation releasing more albumin. Further investigation is needed to unveil the biological significance of that cell behavior.

Block Copolymer Derived Vertically Coupled Plasmonic Arrays for Surface-Enhanced Raman Spectroscopy.

A surface-enhanced Raman spectroscopy sensing template consisting of gold-covered nanopillars is developed. The plasmonic slab consists of a perforated gold film at the base of the nanopillars and a Babinet complementary dot array on top of the pillars. The nanopillars were fabricated by the incorporation of an iron salt precursor into a self-assembled block copolymer thin film and subsequent reactive ion etching. The preparation is easy, scalable, and cost-effective. We report on the increase in surface-enhanced Raman scattering efficiency for smaller pillar heights and stronger coupling between the dot array and perforated gold film with average enhancement factors as high as 107. In addition, the block copolymer-derived templates show an excellent relative standard deviation of 8% in the measurement of the Raman intensity. Finite difference time domain simulations were performed to investigate the nature of the electromagnetic near-field enhancement and to identify plasmonic hot spots.

Engineering State-of-the-Art Plasmonic Nanomaterials for SERS-Based Clinical Liquid Biopsy Applications.

Precision oncology, defined as the use of the molecular understanding of cancer to implement personalized patient treatment, is currently at the heart of revolutionizing oncology practice. Due to the need for repeated molecular tumor analyses in facilitating precision oncology, liquid biopsies, which involve the detection of noninvasive cancer biomarkers in circulation, may be a critical key. Yet, existing liquid biopsy analysis technologies are still undergoing an evolution to address the challenges of analyzing trace quantities of circulating tumor biomarkers reliably and cost effectively. Consequently, the recent emergence of cutting-edge plasmonic nanomaterials represents a paradigm shift in harnessing the unique merits of surface-enhanced Raman scattering (SERS) biosensing platforms for clinical liquid biopsy applications. Herein, an expansive review on the design/synthesis of a new generation of diverse plasmonic nanomaterials, and an updated evaluation of their demonstrated SERS-based uses in liquid biopsies, such as circulating tumor cells, tumor-derived extracellular vesicles, as well as circulating cancer proteins, and tumor nucleic acids is presented. Existing challenges impeding the clinical translation of plasmonic nanomaterials for SERS-based liquid biopsy applications are also identified, and outlooks and insights into advancing this rapidly growing field for practical patient use are provided.

Self-Immolative Fluorescent and Raman Probe for Real-Time Imaging and Quantification of γ-Glutamyl Transpeptidase in Living Cells.

Characterizing over-expressed enzymes or biomarkers in living cells is critical for the molecular understanding of disease pathology and consequently for designing precision medicines. Herein, a "switch-on" probe is designed to selectively detect γ-glutamyl transpeptidase (GGT) in living cells via a unique ensemble of enhanced fluorescence and surface-enhanced Raman scattering (SERS). In the presence of GGT, the γ-glutamyl bond in the probe molecule is cleaved, thereby activating a fluorescent probe molecule as well as a Raman reporter molecule. Consequently, the detection of GGT is achieved based on both plasmonic fluorescent enhancement and SERS with a detection limit as low as 1.2 × 10-3 U/L (normal range for GGT levels in the blood is 9-48 U/L). The main advantage of this platform is that on the occasion of fluorescence signal interference, especially in the presence of free metal ions in cells, the SERS signals still hold high stability as a backup. This work highlights the benefits of the marriage of two complimentary sensing techniques into one platform that can overcome the major obstacles of detection of real-time biomarkers and imaging in living cells.

Coexistence of Different Charge-Transfer Mechanisms in the Hot-Carrier Dynamics of Hybrid Plasmonic Nanomaterials.

Hot-carrier dynamics at the interfaces of semiconductors and nanoclusters is of significant importance for photovoltaic and photocatalytic applications. Plasmon-driven charge separation processes are considered to be only dependent on the type of donor-acceptor interactions, that is, the conventional hot-electron-transfer mechanism for van der Waals interactions and the plasmon-induced interfacial charge-transfer transition mechanism for chemical bonds. Here, we demonstrate that the two mechanisms can coexist in a nanoparticle-semiconductor hybrid nanomaterial, both leading to faster transfer than carrier relaxation. The origin of the two mechanisms is attributed to the spatial polarization of the excited hot carriers, where the longitudinal state couples to semiconductors more strongly than the transverse state. Our findings provide a new insight into the photoinduced carrier dynamics, which is relevant for many applications in solar energy conversion, including efficient water splitting, photocatalysis, and photovoltaics.

DNA-Decorated, Helically Twisted Nanoribbons: A Scaffold for the Fabrication of One-Dimensional, Chiral, Plasmonic Nanostructures.

Crafting of chiral plasmonic nanostructures is extremely important and challenging. DNA-directed organization of nanoparticle on a chiral template is the most appealing strategy for this purpose. Herein, we report a supramolecular approach for the design of DNA-decorated, helically twisted nanoribbons through the amphiphilicity-driven self-assembly of a new class of amphiphiles derived from DNA and hexaphenylbenzene (HPB). The ribbons are self-assembled in a lamellar fashion through the hydrophobic interactions of HPB. The transfer of molecular chirality of ssDNA into the HPB core results in the bias of one of the chiral propeller conformations for HPB and induces a helical twist into the lamellar packing, and leads to the formation of DNA-wrapped nanoribbons with M-helicity. The potential of the ribbon to act as a reversible template for the 1D chiral organization of plasmonic nanomaterials through DNA hybridization is demonstrated.

Plasmonic carbon nanohybrids for repetitive and highly localized photothermal cancer therapy.

Integrating metallic and non-metallic platform for cancer nanomedicine is a challenging task and bringing together multi-functionality of two interfaces is a major hurdle for biomaterial design. Herein, NIR light responsive advanced hybrid plasmonic carbon nanomaterials are synthesized, and their properties toward repetitive and highly localized photothermal cancer therapy are well understood. Graphene oxide nanosheets having thickness of ∼2 nm are synthesized using modified Hummers' method, thereafter functionalized with biodegradable NIR light responsive gold deposited plasmonic polylactic-co-glycolic acid nanoshells (AuPLGA NS, tuned at 808 nm) and NIR dye (IR780) to examine their repetitive and localized therapeutic efficacy as well resulting side effects to nearby healthy cells. It is observed that AuPLGA NS decorated graphene oxide nanosheets (GO-AuPLGA) and IR780 loaded graphene oxide nanosheets (GO-IR780) are capable in standalone complete photothermal ablation of cancer cells within 4 min. of 808 nm NIR laser irradiation and also without the aid of any anticancer drugs. However, GO-AuPLGA having the potential for repetitive photothermal treatment of a big tumor, ablate the cancer cells in highly localized fashion, without having side effects on neighboring healthy cells.