Flexible nanoplasmonic sensor for multiplexed and rapid quantitative food safety analysis with a thousand-times sensitivity improvement.

The accumulation of trace amounts of certain small molecules in food poses considerable human health challenges, including the potential for carcinogenesis and mutagenesis. Here, an ultrasensitive gold-platinum nanoflower-coupled metasurface plasmon resonance (MetaSPR) (APNMSPR) biosensor, based on a competitive immunoassay, was developed for the multiplexed and rapid quantitative analysis of trace small molecules in eggs, offering timely monitoring of food safety. This one-step biosensor can be integrated into either a newly designed detachable high-throughput MetaSPR chip-strip plate device or a standard 96-well plate for multiplexed small-molecule detection within a single egg. The limits of detection were 0.81, 1.12, and 1.74 ppt for florfenicol, fipronil, and enrofloxacin, respectively, demonstrating up to 1000-fold increased sensitivity and a 15-fold reduction in analysis time compared with those of traditional methods. The results obtained using the APNMSPR biosensor showed a strong correlation with those obtained using liquid chromatography-tandem mass spectrometry. The APNMSPR biosensor holds immense promise for the multiplexed, highly sensitive, and rapid quantitative analysis of small molecules for applications in food safety control, early diagnosis, and environmental monitoring.

Application of nanoplasmonic biosensors based on nanoarrays in biological and chemical detection.

Technological innovation, cost effectiveness, and miniaturization are key factors that determine the commercial adaptability and sustainability of sensing platforms. Nanoplasmonic biosensors based on nanocup or nanohole arrays are attractive for the development of various miniaturized devices for clinical diagnostics, health management, and environmental monitoring. In this review, we discuss the latest trends in the engineering and development of nanoplasmonic sensors as biodiagnostic tools for the highly sensitive detection of chemical and biological analytes. We focused on studies that have explored flexible nanosurface plasmon resonance systems using a sample and scalable detection approach in an effort to highlight multiplexed measurements and portable point-of-care applications.

Nanozyme-Catalyzed Metasurface Plasmon Sensor-Based Portable Ultrasensitive Optical Quantification Platform for Cancer Biomarker Screening.

Developing plasmonic biosensors that are low-cost, portable, and relatively simple to operate remains challenging. Herein, a novel metasurface plasmon-etch immunosensor is described, namely a nanozyme-linked immunosorbent surface plasmon resonance biosensor, for the ultrasensitive and specific detection of cancer biomarkers. Gold-silver composite nano cup array metasurface plasmon resonance chip and artificial nanozyme-labeled antibody are used in two-way sandwich analyte detection. Changes in the biosensor's absorption spectrum are measured before and after chip surface etching, which can be applied to immunoassays without requiring separation or amplification. The device achieved a limit of alpha-fetoprotein (AFP) detection < 21.74 fM, three orders of magnitude lower than that of commercial enzyme-linked immunosorbent assay kits. Additionally, carcinoembryonic antigen (CEA) and carbohydrate antigen 125 (CA125) are used for quantitative detection to verify the universality of the platform. More importantly, the accuracy of the platform is verified using 60 clinical samples; compared with the hospital results, the three biomarkers achieve high sensitivity (CEA: 95.7%; CA125: 90.9%; AFP: 86.7%) and specificity (CEA: 97.3%; CA125: 93.9%; AFP: 97.8%). Due to its rapidity, ease of use, and high throughput, the platform has the potential for high-throughput rapid detection to facilitate cancer screening or early diagnostic testing in biosensing.

Dual AuNPs detecting probe enhanced the NanoSPR effect for the high-throughput detection of the cancer microRNA21 biomarker.

The microRNA21 (miR-21), a specific tumor biomarker, is crucial for the diagnosis of several cancer types, and investigation of its overexpression pattern is important for cancer diagnosis. Herein, we report a low-cost, rapid, ultrasensitive, and convenient biosensing strategy for the detection of miR-21 using a nanoplasmonic array chip coupled with gold nanoparticles (AuNPs). This sensing platform combines the surface plasmon resonance effect of nanoplasmonics (NanoSPR) and the localized surface plasmon resonance (LSPR) effect, which allows the real-time monitoring of the subtle optical density (OD) changes caused by the variations in the dielectric constant in the process of the hybridization of the target miRNA. Using this method, the miRNA achieves a broad detection range from 100 aM to 1 µM, and with a limit of detection (LoD) of 1.85 aM. Furthermore, this assay also has a single-base resolution to discriminate the highly homologous miRNAs. More importantly, this platform has high throughput characteristics (96 samples can be detected simultaneously). This strategy exhibits more than 86.5 times enhancement in terms of sensitivity compared to that of traditional biosensors.

An ultra-sensitive and specific nanoplasmonic-enhanced isothermal amplification platform for the ultrafast point-of-care testing of SARS-CoV-2.

The novel mutations attributed by the high mutagenicity of the SARS-CoV-2 makes its prevention and treatment challenging. Developing an ultra-fast, point-of-care-test (POCT) protocol is critical for responding to large-scale spread of SARS-CoV-2 in public places and in resource-poor remote areas. Here, we developed a nanoplasmonic enhanced isothermal amplification (NanoPEIA) strategy that combines a nanoplasmonic sensor with isothermal amplification. The novel strategy provides an ideal easy-to operate detection platform for obtaining accurate, ultra-fast and high-throughput (96 samples can be tested together) data. For clinical samples with viral detection at Ct value <25, the entire process (including sample preparation, virus lysis, detection, and data analysis) can be completed within six minutes. The method is also appropriate for detection of SARS-CoV-2 γ-coronavirus mutants. The NanoPEIA method was validated using clinical samples from 21 patients with SARS-CoV-2 infection and 31 healthy individuals. The detection result on the 52 clinical samples for SARS-CoV-2 showed that the NanoPEIA platform had a 100% sensitivity for N and orf1ab genes, which was higher than those obtained using RT-qPCR (88.9% and 90.0%, respectively). The specificities of 31 clinical negative samples were 92.3% and 91.7% for the N gene and the orf1ab gene, respectively. The limits of detection (LoD) of the clinical samples were 28.3 copies/mL and 23.3 copies/mL for the N gene and the orf1ab gene, respectively. The efficient NanoPEIA detection strategy facilitates real-time detection and visualization within ultrashort durations and can be applied for POCT diagnosis in resource-poor and highly populated areas.

Versatile nanorobot hand biosensor for specific capture and ultrasensitive quantification of viral nanoparticles.

Accurate determination of the concentration and viability of the viral vaccine vectors is urgently needed for preventing the spread of the viral infections, but also supporting the development and assessment of recombinant virus-vectored vaccines. Herein, we describe a nanoplasmonic biosensor with nanoscale robot hand structure (Nano RHB) for the rapid, direct, and specific capture and quantification of adenovirus particles. The nanorobot allows simple operation in practical applications, such as real-time monitoring of vaccine quantity and quality, and evaluation of vaccine viability. Modification of the Nano RHB with branched gold nanostructures allow rapid and efficient assessment of human adenovirus viability, with ultrahigh detection sensitivity of only 100 copies/mL through one-step sandwich method. Nano RHB detection results were consistent with those from the gold standard median tissue culture infectious dose and real-time polymerase chain reaction assays. Additionally, the Nano RHB platform showed high detection specificity for different types of viral vectors and pseudoviruses. Altogether, these results demonstrate that the Nano RHB platform is a promising tool for efficient and ultrasensitive assessment of vaccines and gene delivery vectors.

One-Step Rapid and Sensitive ASFV p30 Antibody Detection via Nanoplasmonic Biosensors.

African swine fever (ASF) is one of the most serious transnational swine diseases in the world. The case fatality rate of susceptible pigs is up to 100%. Currently, no commercial vaccine is available, so the prevention and control of ASF mainly relies on early diagnosis and culling of infected pigs. As the ASF virus continues to evolve, develop, and diversify, nucleic acid testing becomes less efficient. Here, we developed a method for the rapid and direct optical measurement of African swine fever virus (ASFV) antibody in vitro. This one-step procedure requires nearly no sample preparation and involves p30 protein-specific label-free integration into standard 96-well plates. Using a nanoplasmonic biosensor with extraordinary optical transmission (EOT) effect, one-step sample addition, ASFV antibody was detected within 20 min. The positive antibody showed a satisfactory sensitivity and linear relationship in the dilution ratio of 1:100-1:16000. It was used for the detection of clinical serum samples with a coincidence rate of 96.6%. The measurement results can be automatically analyzed and displayed on a conventional microplate meter computer and connected device. Our detection method can be widely applied in point-of-care testing (POCT) of ASFV antibody in pig farms. IMPORTANCE African swine fever (ASF) is a serious transnational disease caused by the African swine fever virus (ASFV), which is highly contagious in wild boars and domestic pigs. There is currently no available vaccine for ASF; therefore, development efforts are a key priority as ASFV continues to evolve and diversify. The ASF antibody rapid detection platform comprising the nanoplasmonic biosensor with extraordinary optical transmission effect can greatly reduce the detection time and improve detection flux while maintaining detection sensitivity and specificity. The one-step sample addition can effectively avoid cross contamination of samples in the detection process. The detection method provides a solution for the rapid and accurate real-time monitoring of ASF in pig farms.

Reactive oxygen species-responsive and Raman-traceable hydrogel combining photodynamic and immune therapy for postsurgical cancer treatment.

Combining immune checkpoint blockade (ICB) therapy with photodynamic therapy (PDT) holds great potential in treating immunologically "cold" tumors, but photo-generated reactive oxygen species (ROS) can inevitably damage co-administered ICB antibodies, hence hampering the therapeutic outcome. Here we create a ROS-responsive hydrogel to realize the sustained co-delivery of photosensitizers and ICB antibodies. During PDT, the hydrogel skeleton poly(deca-4,6-diynedioic acid) (PDDA) protects ICB antibodies by scavenging the harmful ROS, and at the same time, triggers the gradual degradation of the hydrogel to release the drugs in a controlled manner. More interestingly, we can visualize the ROS-responsive hydrogel degradation by Raman imaging, given the ultrastrong and degradation-correlative Raman signal of PDDA in the cellular silent window. A single administration of the hydrogel not only completely inhibits the long-term postoperative recurrence and metastasis of 4T1-tumor-bearing mice, but also effectively restrains the growth of re-challenged tumors. The PDDA-based ROS-responsive hydrogel herein paves a promising way for the durable synergy of PDT and ICB therapy.

Novel nanostructure-coupled biosensor platform for one-step high-throughput quantification of serum neutralizing antibody after COVID-19 vaccination.

COVID-19 vaccination efficacy depends on serum levels of the neutralizing antibodies (NAs) specific to the receptor-binding domain of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Therefore, a high-throughput rapid assay capable of measuring the total SARS-CoV-2 NA level is urgently needed for COVID-19 serodiagnosis, convalescent plasma therapy, vaccine development, and assessment. Here, we developed a novel nanoplasmonic immunosorbent assay (NanoPISA) platform for one-step rapid quantification of SARS-CoV-2 NAs in clinical serum samples for high-throughput evaluation of COVID-19 vaccine effectiveness. The NanoPISA platform enhanced by the use of nanoporous hollow gold nanoparticle coupling was able to detect SARS-CoV-2 NAs with a limit of detection of 0.2 pM within 15 min without washing steps. The one-step NanoPISA for SARS-CoV-2 NA detection in clinical specimens yielded good results, comparable with those obtained in the gold-standard seroneutralization test and the surrogate virus-neutralizing enzyme-linked immunosorbent assay. Collectively, the one-step NanoPISA might be a rapid and high-throughput NA-quantification platform for evaluating the effectiveness of COVID-19 vaccines.

One-step rapid quantification of SARS-CoV-2 virus particles via low-cost nanoplasmonic sensors in generic microplate reader and point-of-care device.

The spread of SARS-CoV-2 virus in the ongoing global pandemic has led to infections of millions of people and losses of many lives. The rapid, accurate and convenient SARS-CoV-2 virus detection is crucial for controlling and stopping the pandemic. Diagnosis of patients in the early stage infection are so far limited to viral nucleic acid or antigen detection in human nasopharyngeal swab or saliva samples. Here we developed a method for rapid and direct optical measurement of SARS-CoV-2 virus particles in one step nearly without any sample preparation using a spike protein specific nanoplasmonic resonance sensor. As low as 370 vp/mL were detected in one step within 15 min and the virus concentration can be quantified linearly in the range of 0 to 107 vp/mL. Measurements shown on both generic microplate reader and a handheld smartphone connected device suggest that our low-cost and rapid detection method may be adopted quickly under both regular clinical environment and resource-limited settings.

Cell spreading and viability on zein films may be facilitated by transglutaminase.

Zein is a biocompatible corn protein potentially useful in the development of biomaterials. In this study, the deposition of zein on oxygen plasma treated glass cover slips significantly enhanced cell spreading and viability. The mechanism for cellular response to zein coated surfaces was thought to involve the polyglutamine peptides on the zein structure. We hypothesized that zein was a substrate for tissue transglutaminase (tTG), an extracellular enzyme involved in cell-surface interactions. SDS-PAGE results suggested an interaction between zein and tTG, where zein was the glutamine donor. Cross-linking between zein and tTG may be the first step in successful cell adhesion and spreading.

Label-free and highly sensitive biomolecular detection using SERS and electrokinetic preconcentration.

In this paper, we present a method combining surface-enhanced Raman scattering (SERS) spectroscopy to detect biomolecules in a label-free way with an electrokinetic preconcentration technique (electrophoresis) to amplify biomolecular signals at low concentrations. A constant electric field is applied to charged biomolecules in solution, attracting them to an oppositely charged electrode, which is also used as a SERS substrate. Within 5 min, we observed that the SERS signal of 10 fM adenine was amplified to the level of the signal of non-preconcentrated 1 microM adenine (sensitivity improvement by 8 orders of magnitude) and the method was effective over a wide range of concentrations (10 fM to 1 microM). The signals were further amplified under stronger electric field and longer application: The increase of the signal intensity was observed to be 51 times at -0.6 V cm(-1) after 25 min. The effectiveness of this method allows the creation of label-free, target-specific, and highly sensitive monitoring applications.

Picomolar sensitivity MRI and photoacoustic imaging of cobalt nanoparticles.

Multimodality imaging based on complementary detection principles has broad clinical applications and promises to improve the accuracy of medical diagnosis. This means that a tracer particle advantageously incorporates multiple functionalities into a single delivery vehicle. In the present work, we explore a unique combination of MRI and photoacoustic tomography (PAT) to detect picomolar concentrations of nanoparticles. The nanoconstruct consists of ferromagnetic (Co) particles coated with gold (Au) for biocompatibility and a unique shape that enables optical absorption over a broad range of frequencies. The end result is a dual-modality probe useful for the detection of trace amounts of nanoparticles in biological tissues, in which MRI provides volume detection, whereas PAT performs edge detection.

Peptide-nanoparticle hybrid SERS probes for optical detection of protease activity.

Real-time in situ detection of active proteases is crucial for early-stage cancer screening and cell signaling pathway study; however, it is difficult to achieve using fluorescence or radioactive probes at volumes below 1 nL. Here we demonstrated a hybrid optical probe by incorporating nanocrescent particle and peptides with artificial tag molecules. We performed a proof-of-concept study using prostate specific antigen (PSA), one of the most prominent prostate cancer markers, and a serine protease present in patients' seminal fluid and serum. The Raman spectral signal from the tag molecules is enhanced by the nanocrescent and the signal is monitored as the indicator for peptide cleavage in a femtoliter reaction volume, at levels close to a single proteolytically active PSA molecule. The high reaction specificity of the peptides on individual nanoparticles minimizes the false detection of other serine proteases and background Raman signal, which results in a high-fidelity and high-signal-to-noise-ratio cancer nanoprobe that can be easily incorporated into nano/microfluidic devices.

Optofluidic control using photothermal nanoparticles.

Photothermal metallic nanoparticles have attracted significant attention owing to their energy-conversion properties. Here, we introduce an optofluidic application based on a direct optical-to-hydrodynamic energy conversion using suspended photothermal nanoparticles near the liquid-air interface. Using light beams with submilliwatt power, we can drive and guide liquid flow in microfluidic channels to transport biomolecules and living cells at controlled speeds and directions. Previously, a variety of methods for controlling microscale liquid flow have been developed owing to the increasing interest for microfluidics-based biochemical analysis systems. However, our method dispenses with the need for complex pump and valve devices, surface chemistry and electrode patterning, or any other further effort towards substrate fabrication. Instead, our optofluidic control method will allow the fabrication of all-optical large-scale integrated microfluidic circuits for biomolecular and cellular processing without any physical valve or mechanical pumping device.

Peptide-nanoparticle hybrid SERS probe for dynamic detection of active cancer biomarker enzymes.

Real-time in situ detection of protease enzymes is crucial for early-stage cancer screening and cell signaling pathway study; however it is difficult to be realized using fluorescence or radioactive probes. Here we devise a hybrid optical probe by incorporating nanocrescent particle and peptides with artificial tag molecules. The peptides have high specificity to PSA, one of the most prominent prostate cancer markers, and a serine protease present in patients' seminal fluid and serum. The extrinsic Raman spectral signal from the tag molecules is enhanced by the nanocrescent and the signal is monitored as the indicator for the peptide digestion in nanomolar PSA concentration and femtoliter reaction volume. Sensitive detection of cancer-related serine protease activity of PSA proteins in low concentrations and small volumes of biofluid is critical to early cancer diagnosis, clinical staging, and therapy. The high reaction specificity of the peptide and the monitored extrinsic Raman signal also minimizes the false detection of other serine proteases and intrinsic Raman signal, which results in a high-fidelity and high-signal-to-noise-ratio cancer nanoprobe. Peptide-conjugated nanocrescents should also be applicable for measuring the intercellular and intracellular activity of other cancer-related proteases and protease activity profiling-enabled cancer cell identification.

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate.

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.

Nanophotonic crescent moon structures with sharp edge for ultrasensitive biomolecular detection by local electromagnetic field enhancement effect.

We present novel gold nanophotonic crescent moon structures with a sub-10 nm sharp edge, which can enhance local electromagnetic field at the edge area. The formation of unconventional nanophotonic crescent moon structure is accomplished by using a sacrificial nanosphere template and conventional thin film deposition method, which allows an effective batch nanofabrication and precise controls of nanostructure shapes. Unique multiple scattering peaks are observed in a single gold nanocrescent moon with dark-field white light illumination. A 785 nm near-infrared (NIR) diode laser was used as the excitation source to induce the amplified scattering field on the sharp edge of the single gold nanocrescent moon. The Raman scattering spectrum of Rhodamine 6G molecules adsorbed on the single gold nanocrescent moon are characterized, and the Raman enhancement factor of single gold nanocrescent moon is estimated larger than 10(10), which suggests the potential applications of gold nanocrescent moons in ultrasensitive biomolecular detection and cellular imaging using surface enhanced Raman spectroscopy.

Time-resolved optical sensing of oligonucleotide hybridization via Au colloidal nanoparticles.

Au nanoparticles have distinctive absorption spectra whose peak position or particle plasmon resonance wavelength is highly sensitive to molecule adsorption on their surfaces. Spherical Au nanoparticles are surface-modified by amino-functionalized self-assembly-monolayer and used as optical probes in the fluorescence-label-free spectroscopic detection of sub-nanomole oligonucleotides. Time-resolved studies of the immobilization and hybridization of oligonucleotides on the surface of Au nanoparticles were carried out. By measuring peak shift of absorption spectra of the Au colloidal nanoparticles over time, the samples of 15 nM 20 mer target and mismatched oligonucleotides are distinguished by their different influences on the particle plasmon resonance wavelength. The approach presented in this paper extends the application of Au nanoparticles as the optical probe in oligonucleotide recognitions without prior sample labeling.