Wearable Plasmonic Sweat Biosensor for Acetaminophen Drug Monitoring

Monitoring the acetaminophen dosage is important to prevent the occurrence of adverse reactions such as liver failure and kidney damage. Traditional approaches to monitoring acetaminophen dosage mainly rely on invasive blood collection. Herein, we developed a noninvasive microfluidic-based wearable plasmonic sensor to achieve simultaneous sweat sampling and acetaminophen drug monitoring for vital signs. The fabricated sensor employs an Au nanosphere cone array as the key sensing component, which poses a substrate with surface-enhanced Raman scattering (SERS) activity to noninvasively and sensitively detect the fingerprint of acetaminophen molecules based on its unique SERS spectrum. The developed sensor enabled the sensitive detection and quantification of acetaminophen at concentrations as low as 0.13 μM. We further evaluated the sweat sensor integrated with a Raman spectrometer for monitoring acetaminophen in drug-administered subjects. These results indicated that the sweat sensor could measure acetaminophen levels and reflect drug metabolism. The sweat sensors have revolutionized wearable sensing technology by adopting label-free and sensitive molecular tracking methods for noninvasive and point-of-care drug monitoring and management.

Direct Thermal Growth of Gold Nanopearls on 3D Interweaved Hydrophobic Fibers as Ultrasensitive Portable SERS Substrates for Clinical Applications

Surface-enhanced Raman spectroscopy (SERS)-based biosensors have attracted much attention for their label-free detection, ultrahigh sensitivity, and unique molecular fingerprinting. In this study, a wafer-scale, ultrasensitive, highly uniform, paper-based, portable SERS detection platform featuring abundant and dense gold nanopearls with narrow gap distances, are prepared and deposited directly onto ultralow-surface-energy fluorosilane-modified cellulose fibers through simple thermal evaporation by delicately manipulating the atom diffusion behavior. The as-designed paper-based SERS substrate exhibits an extremely high Raman enhancement factor (3.9 × 10¹¹ ), detectability at sub-femtomolar concentrations (single-molecule level) and great signal reproductivity (relative standard deviation: 3.97%), even when operated with a portable 785-nm Raman spectrometer. This system is used for fingerprinting identification of 12 diverse analytes, including clinical medicines (cefazolin, chloramphenicol, levetiracetam, nicotine), pesticides (thiram, paraquat, carbaryl, chlorpyrifos), environmental carcinogens (benzo[a]pyrene, benzo[g,h,i]perylene), and illegal drugs (methamphetamine, mephedrone). The lowest detection concentrations reach the sub-ppb level, highlighted by a low of 16.2 ppq for nicotine. This system appears suitable for clinical applications in, for example, i) therapeutic drug monitoring for individualized medication adjustment and ii) ultra-early diagnosis for pesticide intoxication. Accordingly, such scalable, portable and ultrasensitive fibrous SERS substrates open up new opportunities for practical on-site detection in biofluid analysis, point-of-care diagnostics and precision medicine.

Plasmonic Biosensors with Nanostructure for Healthcare Monitoring and Diseases Diagnosis

Nanophotonics has been widely utilized in enhanced molecularspectroscopy or mediated chemical reaction, which has major applications in the field of enhancing sensing and enables opportunities in developing healthcare monitoring. This review presents an updated overview of the recent exciting advances of plasmonic biosensors in the healthcare area. Manufacturing, enhancements and applications of plasmonic biosensors are discussed, with particular focus on nanolisted main preparation methods of various nanostructures, such as chemical synthesis, lithography, nanosphere lithography, nanoimprint lithography, etc., and describing their respective advances and challenges from practical applications of plasmon biosensors. Based on these sensing structures, different types of plasmonic biosensors are summarized regarding detecting cancer biomarkers, body fluid, temperature, gas and COVID-19. Last, the existing challenges and prospects of plasmonic biosensors combined with machine learning, mega data analysis and prediction are surveyed.

Thickness-Sensing Sandwiched Plasmonic Biosensors Enable Label-Free Naked-Eye Antibody Quantification

Clinical serology assays for detecting the antibodies of the virus are time-consuming, are less sensitive/selective, or rely on sophisticated detection instruments. Here, we develop a sandwiched plasmonic biosensor (SPB) for supersensitive thickness-sensing via utilizing the distance-dependent electromagnetic coupling in sandwiched plasmonic nanostructures. SPBs quantitatively amplify the thickness changes on the nanoscale range (sensitivity: ∼2% nm^-1) into macroscopically visible signals, thereby enabling the rapid, label-free, and naked-eye detection of targeted biomolecular species (via the thickness change caused by immunobinding events). As a proof of concept, this assay affords a broad dynamic range (7 orders of magnitude) and a low LOD (∼0.3 pM), allowing for the extremely accurate SARS-CoV-2 antibody quantification (sensitivity/specificity: 100%/∼99%, with a portable optical fiber device). This strategy is suitable for high-throughput multiplexed detection and smartphone-based sensing at the point-of-care, which can be expanded for various sensing applications beyond the fields of viral infections and vaccination.

Flexible Plasmonic Biosensors for Healthcare Monitoring: Progress and Prospects

The noble metal nanoparticle has been widely utilized as a plasmonic unit to enhance biosensors, by leveraging its electric and/or optical properties. Integrated with the "flexible" feature, it further enables opportunities in developing healthcare products in a conformal and adaptive fashion, such as wrist pulse tracers, body temperature trackers, blood glucose monitors, etc. In this work, we present a holistic review of the recent advance of flexible plasmonic biosensors for the healthcare sector. The technical spectrum broadly covers the design and selection of a flexible substrate, the process to integrate flexible and plasmonic units, the exploration of different types of flexible plasmonic biosensors to monitor human temperature, blood glucose, ions, gas, and motion indicators, as well as their applications for surface-enhanced Raman scattering (SERS) and colorimetric detections. Their fundamental working principles and structural innovations are scoped and summarized. The challenges and prospects are articulated regarding the critical importance for continued progress of flexible plasmonic biosensors to improve living quality.

Entangled Nanoplasmonic Cavities for Estimating Thickness of Surface-Adsorbed Layers

Plasmonic sensors provide real-time and label-free detection of biotargets with unprecedented sensitivity and detection limit. However, they usually lack the ability to estimate the thickness of the target layer formed on top of the sensing surface. Here, we report a sensing modality based on reflection spectroscopy of a nanoplasmonic Fabry-Perot cavity array, which exhibits characteristics of both surface plasmon polaritons and localized plasmon resonances and outperforms its conventional counterparts by providing the thickness of the surface-adsorbed layers. Through numerical simulations, we demonstrate that the designed plasmonic surface resembles two entangled Fabry-Perot cavities excited from both ends. Performance of the device is evaluated by studying sensor response in the refractive index (RI) measurement of aqueous glycerol solutions and during formation of a surface-adsorbed layer consisting of protein (i.e., NeutrAvidin) molecules. By tracking the resonance wavelengths of the two modes of the nanoplasmonic surface, it is therefore possible to measure the thickness of a homogeneous adsorbed layer and RI of the background solution with precisions better than 4 nm and 0.0001 RI units. Using numerical simulations, we show that the thickness estimation algorithm can be extended for layers consisting of nanometric analytes adsorbed on an antibody-coated sensor surface. Furthermore, performance of the device has been evaluated to detect exosomes. By providing a thickness estimation for adsorbed layers and differentiating binding events from background RI variations, this device can potentially supersede conventional plasmonic sensors.

Plasmonic Biosensor Based on Vertical Arrays of Gold Nanoantennas

Implementing large arrays of gold nanowires as functional elements of a plasmonic biosensor is an important task for future medical diagnostic applications. Here we present a microfluidic-channel-integrated sensor for the label-free detection of biomolecules, relying on localized surface plasmon resonances. Large arrays (∼1 cm²) of vertically aligned and densely packed gold nanorods to receive, locally confine, and amplify the external optical signal are used to allow for reliable biosensing. We accomplish this by monitoring the change of the optical nanostructure resonance in the presence of biomolecules within the tight focus area above the nanoantennas, combined with a surface treatment of the nanowires for a specific binding of the target molecules. As a first application, we detect the binding kinetics of two distinct DNA strands as well as the following hybridization of two complementary strands (cDNA) with different lengths (25 and 100 bp). Upon immobilization, a redshift of 1 nm was detected; further backfilling and hybridization led to a peak shift of additional 2 and 5 nm for 25 and 100 bp, respectively. We believe that this work gives deeper insight into the functional understanding and technical implementation of a large array of gold nanowires for future medical applications.

Surface Plasmon Resonance or Biocompatibility-Key Properties for Determining the Applicability of Noble Metal Nanoparticles

Metal and in particular noble metal nanoparticles represent a very special class of materials which can be applied as prepared or as composite materials. In most of the cases, two main properties are exploited in a vast number of publications: biocompatibility and surface plasmon resonance (SPR). For instance, these two important properties are exploitable in plasmonic diagnostics, bioactive glasses/glass ceramics and catalysis. The most frequently applied noble metal nanoparticle that is universally applicable in all the previously mentioned research areas is gold, although in the case of bioactive glasses/glass ceramics, silver and copper nanoparticles are more frequently applied. The composite partners/supports/matrix/scaffolds for these nanoparticles can vary depending on the chosen application (biopolymers, semiconductor-based composites: TiO₂, WO₃, Bi₂WO₆, biomaterials: SiO₂ or P₂O₅-based glasses and glass ceramics, polymers: polyvinyl alcohol (PVA), Gelatin, polyethylene glycol (PEG), polylactic acid (PLA), etc.). The scientific works on these materials' applicability and the development of new approaches will be targeted in the present review, focusing in several cases on the functioning mechanism and on the role of the noble metal.

Metal-Organic Framework as a Protective Coating for Biodiagnostic Chips

Zeolitic imidazolate framework-8 (ZIF-8) grown around antibodies anchored to plasmonic nanostructures serves as a protective layer to preserve the biorecognition ability of antibodies stored at room and elevated temperatures for several days. The biofunctionality of the ZIF-8-protected biochip can be restored by a simple water-rinsing step, making it highly convenient for use in point-of-care and resource-limited settings.

Aromatic Functionality of Target Proteins Influences Monomer Selection for Creating Artificial Antibodies on Plasmonic Biosensors

Natural antibodies used as biorecognition elements suffer from numerous shortcomings, such as limited chemical and environmental stability and cost. Artificial antibodies based on molecular imprinting are an attractive alternative to natural antibodies. We investigated the role of aromatic interactions in target recognition capabilities of artificial antibodies. Three proteins with different aromatic amino acid content were employed as model targets. Artificial antibodies were formed on nanostructures using combinations of silane monomers of varying aromatic functionality. We employed refractive index sensitivity of plasmonic nanostructures as a transduction platform for monitoring various steps in the imprinting process and to quantify the target recognition capabilities of the artificial antibodies. The sensitivity of the artificial antibodies with aromatic interactions exhibited a protein-dependent enhancement. Selectivity and sensitivity enhancement due to the presence of aromatic groups in imprinted polymer matrix was found to be higher for target proteins with higher aromatic amino acid content. Our results indicate that tailoring the monomer composition based on the amino acid content of the target protein can improve the sensitivity of plasmonic biosensors based on artificial antibodies without affecting the selectivity.

Plasmonic sensing using metallic nano-sculptured thin films

Nano-sculptured thin films (nSTFs) is a group of meterials prepared by the oblique or the glancing angle deposition technique. They take the form of rods having different shapes such as nanocolumns, nanoscrews, nanozigzags and many other nanoshapes. Their potential for biosensing is highlighted in this review particularly the metallic ones due to their remarkable plasmonic properties. The techniques that have been shown so far to be of high potential are: extended surface plasmon resonance (SPR), localised SPR, surface enhanced flourescence (SEF) and Raman scattering (SERS). The use of metal nSTFs in SPR biosensors with Kretschmann-Raether configuration enhances both the angular and the spectral sensitivities due to the porosity and adds more degrees of freedom in designing evanescent waves based techniques. The metallic nSTFs, exhibit remarkable localised plasmonic properties that make them a promising substrate for enhanced spectroscopies. Their long term stability in water environment makes them suitable candidates for biosensing in water as it is already demonstrated for several water pollutants. The influences of the nanostructures' size, topology, the substrate features, and the preparation conditions on the enhancement of SEF and SERS are highlighted with emphases on the unresolved issues and future trends.