Self-assembled plasmonic nanoarrays for enhanced bacterial identification and discrimination

Concanavalin-A-assisted extraction-free one-pot RPA-CRISPR/Cas12a assay for rapid detection of HPV16

Human papillomavirus (HPV) infection is a major threat to women's health worldwide. High-risk subtypes, particularly HPV16, require rigorous screening and long-term surveillance to control cervical cancer. However, traditional HPV testing is hampered by the need for nucleic acid extraction, reliance on specialized technicians, and fluorescence detection equipment, limiting its suitability for rapid on-site testing. In this study, we developed a Concanavalin A-assisted extraction-free one-pot recombinase polymerase amplification (RPA) CRISPR/Cas12a assay (ConRCA) for HPV16. Concanavalin A-coated magnetic beads were used for target enrichment and nucleic acid-extraction-free processing. Suboptimal protospacer-adjacent motifs were used to achieve a one-pot RPA-CRISPR/Cas12a assay. The ConRCA assay can be completed in approximately 25 min under isothermal conditions and can detect at least 1.2 copies/μL of HPV16 genomic DNA using a fluorescence reader or test strip, demonstrating comparable sensitivity to qPCR. The feasibility of this detection method was evaluated with 31 unextracted clinical samples. Compared with qPCR, the overall sensitivity was 95% (19/20), and the specificity was 100% (11/11). Our results indicate that the ConRCA assay has great potential utility as a point-of-care testing for the rapid identification of HPV.

Ultrasensitive detection of Vibrio parahaemolyticus based on boric acid-functionalized Eu (III)-based metal-organic framework

This study intends to create a ratiometric fluorescence probe utilizing aptamers for the detection of Vibrio parahaemolyticus (V. parahaemolyticus) in aquatic products. In this design, aptamer-functionalized magnetic nanoparticles specifically capture V. parahaemolyticus, while boric acid on Eu (III)-Based Metal-Organic Framework (Eu-MOF) interacts with glycolipids present on bacterial cells, thereby achieving dual recognition of V. parahaemolyticus. This fluorescent probe quantitatively detects V. parahaemolyticus by measuring the intensity of ratio fluorescence. The sensor demonstrates a detection range from 77 to 7.7 × 107 CFU/mL, possessing a detection threshold down to 1 CFU/mL. Moreover, the developed method based on Eu-MOF had been successfully applied to real samples. To achieve rapid on-site detection of V. parahaemolyticus, the study designed a portable smartphone sensor that confirms its capability for rapidly detecting pathogens and contributes significantly to establishing a system for regulating safety in detecting food and environment.

Bottom-Up Metasurfaces for Biotechnological Applications

Metasurfaces are the 2D counterparts of metamaterials, and their development is accelerating rapidly in the past years. This progress enables the creation of devices capable of uniquely manipulating light, with applications ranging from optical communications to remote biosensing. Metasurfaces are engineered by rational assembly of subwavelength elements, defined as meta-atoms, giving rise to unique physical properties arising from the collective behavior of meta-atoms. These meta-atoms are typically organized using effective, reproducible, and precise nanofabrication methods that require a lot of effort to achieve scalable and cost-effective metasurfaces. In contrast, bottom-up methods based on colloidal nanoparticles (NPs) have developed in the last decade as a fascinating alternative for accelerating the technological spread of metasurfaces. The present review takes stock of recent advances in the fabrication and applications of hybrid metasurfaces prepared by bottom-up methods, resulting in disordered metasurfaces. In particular, metasurfaces prepared with plasmonic NPs are emphasized for their multifold applications, which are discussed from a biotechnology perspective. However, some examples of organized metasurfaces prepared by merging bottom-up and top-down approaches are also described. Finally, leveraging the historical disordered metasurface evolution, the review draws new perspectives for random metasurface design and applications.

Interfacial Self-Assembly Nanostructures: Constructions and Applications

Interfacial self-assembly nanoarrays refer to the spontaneously organized nanostructures at interfaces, relying on the intrinsic properties of involved materials, such as surface energy, molecular structure, and interactions. In recent years, the exponential growth of self-assembly nanotechnology has substantially expanded the utility of nanomaterials. Particularly, non-covalent interactions-based interfacial self-assembly represents a viable and promising approach for the synthesis of novel nanostructure. This review introduces the significance and current development status of interfacial self-assembly technology, focusing on the driving mode, application, and prospects of interfacial self-assembly nanoarrays over the past few years.

Self-Assembled Gold Nanoparticles as Reusable SERS Substrates for Polyphenolic Compound Detection

Natural polyphenolic compounds play a pivotal role in biological processes and exhibit notable antioxidant activity. Among these compounds, chlorogenic acid stands out as one of the most widespread and important polyphenols. The accurate detection of chlorogenic acid is crucial for ensuring the quality and classification of the raw materials used in its extraction, as well as the final products in the food, pharmaceutical, and cosmetics industries that contain this bioactive compound. Raman spectroscopy emerges as a powerful analytical tool, particularly in field applications, due to its versatility and sensitivity, offering both qualitative and quantitative analyses. By using the self-assembly of gold nanoparticles at liquid-liquid interfaces and the developed "aqua-print" process, we propose a facile and inexpensive route to fabricate enhanced substrates for surface-enhanced Raman spectroscopy with high reproducibility. To ensure substrate reliability and accurate molecule detection in SERS experiments, a benchmarking procedure was developed. This process involved the use of non-resonant rhodamine 6G dye in the absence of charge transfer and was applied to all synthesized nanoparticles and fabricated substrates. The latter revealed the highest enhancement factor of 4 × 104 for 72 nm gold nanoparticles among nanoparticle diameters ranging from 14 to 99 nm. Furthermore, the enhanced substrate was implemented in the detection of chlorogenic acid with a concentration range from 10 μM to 350 μM, demonstrating high accuracy (R2 > 99%). Raman mapping was employed to validate the good uniformity of the signal (the standard deviation was below 15%). The findings of this study were also supported by DFT calculations of the theoretical Raman spectra, demonstrating the formation of the chlorogenic acid dimer. The proposed method is strategically important for the development of the class of in-field methods to detect polyphenolic compounds in raw materials such as plants, extracted plant proteins, and polyphenolic compounds.

Self-Assembled Hyperbranched Gold Nanoarrays Decode Serum United Urine Metabolic Fingerprints for Kidney Tumor Diagnosis

Serum united urine metabolic analysis comprehensively reveals the disease status for kidney diseases in particular. Thus, the precise and convenient acquisition of metabolic molecular information from united biofluids is vitally important for clinical disease diagnosis and biomarker discovery. Laser desorption/ionization mass spectrometry (LDI-MS) presents various advantages in metabolic analysis; however, there remain challenges in ionization efficiency and MS signal reproducibility. Herein, we constructed a self-assembled hyperbranched black gold nanoarray (HyBrAuNA) assisted LDI-MS platform to profile serum united urine metabolic fingerprints (S-UMFs) for diagnosis of early stage renal cell carcinoma (RCC). The closely packed HyBrAuNA afforded strong electromagnetic field enhancement and high photothermal conversion efficacy, enabling effective ionization of low abundant metabolites for S-UMF collection. With a uniform nanoarray, the platform presented excellent reproducibility to ensure the accuracy of S-UMFs obtained in seconds. When it was combined with automated machine learning analysis of S-UMFs, early stage RCC patients were discriminated from the healthy controls with an area under the curve (AUC) > 0.99. Furthermore, we screened out a panel of 9 metabolites (4 from serum and 5 from urine) and related pathways toward early stage kidney tumor. In view of its high-throughput, fast analytical speed, and low sample consumption, our platform possesses potential in metabolic profiling of united biofluids for disease diagnosis and pathogenic mechanism exploration.

Host-Guest Self-Assembled Interfacial Nanoarrays for Precise Metabolic Profiling

Accurate and rapid metabolic profiling of cerebrospinal fluid (CSF) is urgently needed but remains challenging for clinical diagnosis of central nervous system diseases and biomarker discovery. Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) holds promise for metabolic analysis. Its low signal reproducibility, however, severely restricts acquisition of quantitative MS data in clinical practice. Herein, a multifunctional self-assembled AuNPs array (MSANA)-based LDI-MS platform for direct amino acids analysis and metabolic profiling in patient CSF samples is developed. MSANA featuring a highly ordered and closely packed two-dimensional nanostructure permits capture and direct analysis of aromatic amino acids by LDI-MS with high selectivity and micromolar sensitivity. Meanwhile, the MSANA-based LDI-MS platform exhibits excellent reproducibility (RSD < 10%), largely outperforming the direct matrix spotting approach widely used now (RSD < 44%). The platform is successfully used in metabolic profiling of CSF (1 µL) within minutes for discrimination of medulloblastoma patients from non-tumor controls. Taken together, the MSANA-based LDI-MS platform shows potential clinical values toward large-scale metabolic diagnostics and pathogenic mechanism study.

Differences between surfactant-free Au@Ag and CTAB-stabilized Au@Ag star-like nanoparticles in the preparation of nanoarrays to improve their surface-enhanced Raman scattering (SERS) performance

In this study, we assessed the controlled synthesis and efficacy of surface-enhanced Raman scattering (SERS) on two distinct types of star-like Au@Ag core-shell nanoarrays. These nanoarrays were designed based on gold nanostars (AuNSs), which were synthesized with and without CTAB surfactant (AuNSs-CTAB and AuNSs-FS, respectively). The AuNS-FS nanoparticles were synthesized via a novel modification process, which helped overcome the previous limitations in the free-surfactant preparation of AuNSs by significantly increasing the number of branches, increasing the sharpness of the branches and minimizing the adsorption of the surfactant on the surface of AuNSs. Furthermore, the differences in the size and morphology of these AuNSs in the created nanoarrays were studied. To create the nanoarrays, a three-step method was employed, which involved the controlled synthesis of gold nanostars, covering them with a silver layer (AuNSs-FS@Ag and AuNSs-CTAB@Ag), and finally self-assembling the AuNS@Ag core-shelled nanoparticles via the liquid/liquid self-assembly method. AuNSs-FS@Ag showed higher ability in forming self-assembled nanoarrays than the nanoparticles prepared using CTAB, which can be attributed to the decrease in the repulsion between the nanoparticles at the interface. The nano-substrates developed with AuNSs-FS@Ag possessed numerous "hot spots" on their surface, resulting in a highly effective SERS performance. AuNSs-FS featured a significantly higher number of sharp branches than AuNSs-CTAB, making it the better choice for creating nanoarrays. It is worth mentioning that AuNSs-CTAB did not exhibit the same benefits as AuNSs-FS. The morphology of AuNSs with numerous branches was formed by controlling the seed boiling temperature and adding a specific amount of silver ions. To compare the SERS activity between the as-prepared nano-substrates, i.e., AuNS-CTAB@Ag and AuNS-FS@Ag self-assembled nanoarrays, low concentrations of crystal violet aqueous solution were characterized. The results showed that the developed AuNSs-FS@Ag could detect CV at trace concentrations ranging from 1.0 ng mL-1 to 10 ng mL-1 with a limit of detection (LOD) of 0.45 ng mL-1 and limit of quantification (LOQ) of 1.38 ng mL-1. The nano-substrates remained stable for 42 days with a decrease in the intensity of the characteristic Raman peaks of CV by less than 7.0% after storage. Furthermore, the spiking method could detect trace amounts of CV in natural water from the Dong Nai River with concentrations as low as 1 to 100 ng mL-1, with an LOD of 6.07 ng mL-1 and LOQ of 18.4 ng mL-1. This method also displayed good reproducibility with an RSD value of 5.71%. To better understand the impact of CTAB stabilization of the Au@Ag star-like nanoparticles on their surface-enhanced Raman scattering (SERS) performance, we conducted density functional theory (DFT) calculations. Our research showed that the preparation of AuNSs-FS@Ag via self-assembly is an efficient, simple, and fast process, which can be easily performed in any laboratory. Furthermore, the research and development results presented herein on nanoarrays have potential application in analyzing and determining trace amounts of organic compounds in textile dyeing wastewater.

Combining surface-accessible Ag and Au colloidal nanomaterials with SERS for in situ analysis of molecule-metal interactions in complex solution environments

The interactions between molecules and noble metal nanosurfaces play a central role in many areas of nanotechnology. The surface chemistry of noble metal surfaces under ideal, clean conditions has been extensively studied; however, clean conditions are seldom met in real-world applications. We developed a sensitive and robust characterization technique for probing the surface chemistry of nanomaterials in the complex environments that are directly relevant to their applications. Surface-enhanced Raman spectroscopy (SERS) can be used to probe the interaction of plasmonic nanoparticles with light to enhance the Raman signals of molecules near the surface of nanoparticles. Here, we explain how to couple SERS with surface-accessible plasmonic-enhancing substrates, which are capped with weakly adsorbing capping ligands such as citrate and chloride ions, to allow molecule-metal interactions to be probed in situ and in real time, thus providing information on the surface orientation and the formation and breaking of chemical bonds. The procedure covers the synthesis and characterization of surface-accessible colloids, the preliminary SERS screening with agglomerated colloids, the synthesis and characterization of interfacial nanoparticle assemblies, termed metal liquid-like films, and the in situ biphasic SERS analysis with metal liquid-like films. The applications of the approach are illustrated using two examples: the probing of π-metal interactions and that of target/ligand-particle interactions on hollow bimetallic nanostars. This protocol, from the initial synthesis of the surface-accessible plasmonic nanoparticles to the final in situ biphasic SERS analysis, requires ~14 h and is ideally suited to users with basic knowledge in performing Raman spectroscopy and wet synthesis of metal nanoparticles.

A signal-off aptasensor for the determination of Acinetobacter baumannii by using methylene blue as an electrochemical probe

An electrochemical aptasensor has been developed to detect Acinetobacter baumannii (A. baumannii). The proposed system was developed by modifying carbon screen-printed electrodes (CSPEs) with a synthesized MWCNT@Fe₃O₄@SiO₂-Cl nanocomposite and then binding A. baumannii-specific aptamer using covalent immobilization on the modified electrode surface and the interaction of methylene blue (MB) with Apt as an electrochemical redox indicator. As a result of the incubation of the A. baumannii bacteria as a target on the proposed aptasensor, a cathodic peak current density (J_pc) of MB decreased due to the formation of the Apt-A. baumannii complex and MB being released from the immobilized Apt on the surface of the modified electrode. In addition to increasing the electron transfer kinetics, the nanocomposite provides a relatively stable matrix to improve the loading Apt sequence. The suggested aptasensor was demonstrated to be capable of detecting A. baumannii with a linear range of 10.0-1.0 × 10⁷ colony-forming unit (CFU) mL^-1 and a detection limit of 1 CFU mL^-1 (S/N = 3) using differential pulse voltammetry (DPV) studies at a working potential of ~0.29 V and a scan rate of 100 mV s^-1. The outcomes revealed that the aptasensor exhibited high A. baumannii detection sensitivity, stability, reproducibility, and specificity.

Polyaniline-based 3D network structure promotes entrapment and detection of drug-resistant bacteria

Sensitive and accurate capture, enrichment, and identification of drug-resistant bacteria on human skin are important for early-stage diagnosis and treatment of patients. Herein, we constructed a three-dimensional hierarchically structured polyaniline nanoweb (3D HPN) to capture, enrich, and detect drug-resistant bacteria on-site by rubbing infected skins. These unique hierarchical nanostructures enhance bacteria capture efficiency and help severely deform the surface of the bacteria entrapped on them. Therefore, 3D HPN significantly contributes to the effective and reliable recovery of drug-resistant bacteria from the infected skin and the prevention of potential secondary infection. The recovered bacteria were successfully identified by subsequent real-time polymerase chain reaction (PCR) analysis after the lysis process. The molecular analysis results based on a real-time PCR exhibit excellent sensitivity to detecting target bacteria of concentrations ranging from 102 to 107 CFU/mL without any fluorescent signal interruption. To confirm the field applicability of 3D HPN, it was tested with a drug-resistant model consisting of micropig skin similar to human skin and Klebsiella pneumoniae carbapenemase-producing carbapenem-resistant Enterobacteriaceae (KPC-CRE). The results show that the detection sensitivity of this assay is 102 CFU/mL. Therefore, 3D HPN can be extended to on-site pathogen detection systems, along with rapid molecular diagnostics through a simple method, to recover KPC-CRE from the skin.

Recent advances of Raman spectroscopy for the analysis of bacteria

Rapid and sensitive bacteria detection and identification are becoming increasingly important for a wide range of areas including the control of food safety, the prevention of infectious diseases, and environmental monitoring. Raman spectroscopy is an emerging technology which provides comprehensive information for the analysis of bacteria in a short time and with high sensitivity. Raman spectroscopy offers many advantages including relatively simple operation, non-destructive analysis, and information on molecular differences between bacteria species and strains. A variety of biochemical properties can be measured in a single spectrum. This short review covers the recent advancements and applications of Raman spectroscopy for bacteria analysis with specific focuses on bacteria detection, bacteria identification and discrimination, as well as bacteria antibiotic susceptibility testing in 2022. The development of novel substrates, the combination with other techniques, and the utilization of advanced data processing tools for the improvement of Raman spectroscopy and future directions are discussed.

A ratiometric SERS aptasensor array for human DNA glycosylaseat single-cell sensitivity/resolution

Human 8-oxoguanine DNA glycosylase (hOGG1) is involved in the cellular genomic 8-oxoguanine (8-oxoG) excision repair to maintain genome stability. Accurate detection of hOGG1 activity is essential for clinical diagnosis and treatment of various human pathology. Yet, the quantitative detection of hOGG1 remains challenging for existing methods due to poor reproducibility and portability. Herein, we propose a ratiometric array-based SERS point-of-care testing method for hOGG1 activity. A kind of reproducible, uniform and stable plasmonic multi-microarray reaction cells was constructed by assembling AuNPs on the substrate modified by aminosilane and segmented by silica gel gasket, which greatly improved the sensitivity, portability and repeatability of SERS measurement. Based on this, the ratiometric method is further used to effectively overcome the instability of single SERS signal intensity, which allows signal rationing and provides built-in correction for environment effects. In specific, we designed two different Raman-labeled probes for the detection of hOGG1, a thiol- and Cy3-labeled aptamer as an internal standard and a Rox-labeled 8-oxoG-modified complementary aptamer as a signal probe. The ratio value between Cy3 and Rox SERS intensity is well linear with the hOGG1 activity on logarithmic scales in the range from 5 × 10^-5 to 5 × 10^-3 U/mL, and the limit of detection reaches 3.3 × 10^-5 U/mL. Moreover, this strategy can be applied for the screening of inhibitors and the monitoring of cellular hOGG1 activity fluctuation at single-cell levels, providing a flexible and adaptive tool for clinical diagnosis, biochemical processes and drug discovery.

Dual Synthetic Receptor-Based Sandwich Electrochemical Sensor for Highly Selective and Ultrasensitive Detection of Pathogenic Bacteria at the Single-Cell Level

Sensitive and rapid detection of pathogenic bacteria is essential for effective source control and prevention of microbial infectious diseases. However, it remains a substantial challenge to rapidly detect bacteria at the single-cell level. Herein, we present an electrochemical sandwich sensor for highly selective and ultrasensitive detection of a single bacterial cell based on dual recognition by the bacteria-imprinted polymer film (BIF) and aptamer. The BIF was used as the capture probe, which was in situ fabricated on the electrode surface within 15 min via electropolymerization. The aptamer and electroactive 6-(Ferrocenyl)hexanethiol cofunctionalized gold nanoparticles (Au@Fc-Apt) were employed as the signal probe. Once the target bacteria were anchored on the BIF-modified electrode, the Au@Fc-Apt was further specifically bound to the bacteria, generating enhanced current signals for ultrasensitive detection of Staphylococcus aureus down to a single cell in phosphate buffer solution. Even in the complex milk samples, the sensor could detect as low as 10 CFU mL^-1 of S. aureus without any complicated pretreatment except for 10-fold dilution. Moreover, the current response to the target bacteria was hardly affected by the coexisting multiple interfering bacteria, whose number is 30 times higher than the target, demonstrating the excellent selectivity of the sensor. Compared with most reported sandwich-type electrochemical sensors, this assay is more sensitive and more rapid, requiring less time (1.5 h) for the sensing interface construction. By virtue of its sensitivity, rapidity, selectivity, and cost-effectiveness, the sensor can serve as a universal detection platform for monitoring pathogenic bacteria in fields of food/public safety.

DNA-Guided One-Dimensional Plasmonic Nanostructures for the SERS Bioassay

Plasmonic nanostructures have a desirable surface-enhanced Raman scattering (SERS) response related to particle spacing. However, precisely controlling the distance of plasmonic nanostructures is still a challenge. DNA has the merit of specific recognition, and flexible modification of functional groups, which can be used to flexibly adjust the gaps between plasmonic nanostructures for improving the stability of SERS. In this paper, DNA-guided gold nanoparticles formed one-dimensional ordered structures and they were self-assembled at the water-oil interface by a bottom-up approach. Notably, an output switching strategy successfully transfers a small amount of target into a large amount of reporter DNA; thereby, Raman probes are captured on the sensing interface and achieve the SERS assay of microRNA 155 (miRNA-155). This study is an exciting strategy for obtaining ordered plasmonic structures and providing surveillance, which is important for the clinical diagnosis of early-stage cancer.

Combining Acoustic Bioprinting with AI-Assisted Raman Spectroscopy for High-Throughput Identification of Bacteria in Blood

Identifying pathogens in complex samples such as blood, urine, and wastewater is critical to detect infection and inform optimal treatment. Surface-enhanced Raman spectroscopy (SERS) and machine learning (ML) can distinguish among multiple pathogen species, but processing complex fluid samples to sensitively and specifically detect pathogens remains an outstanding challenge. Here, we develop an acoustic bioprinter to digitize samples into millions of droplets, each containing just a few cells, which are identified with SERS and ML. We demonstrate rapid printing of 2 pL droplets from solutions containing S. epidermidis, E. coli, and blood; when they are mixed with gold nanorods (GNRs), SERS enhancements of up to 1500× are achieved.We then train a ML model and achieve ≥99% classification accuracy from cellularly pure samples and ≥87% accuracy from cellularly mixed samples. We also obtain ≥90% accuracy from droplets with pathogen:blood cell ratios <1. Our combined bioprinting and SERS platform could accelerate rapid, sensitive pathogen detection in clinical, environmental, and industrial settings.

Ultrasensitive detection of β-lactamase-associated drug-resistant bacteria using a novel mass-tagged probe-mediated cascaded signal amplification strategy

The emergence and spread of drug-resistant bacteria (DRB) is a global health threat. Early and accurate detection of DRB is a critical step in the treatment of DRB infection. However, traditional assays for DRB detection are time-consuming and have inferior analytical sensitivity and quantification capability. Herein, a mass-tagged probe (MP-CMSA)-mediated enzyme- and light-assisted cascaded signal amplification strategy was developed for the ultrasensitive detection of β-lactamase (BLA), an enzyme closely associated with most DRB. Each MP-CMSA probe contained multiple poly(amidoamine) (PAMAM) dendrimer molecules immobilized on a streptavidin agarose bead via a BLA-cleavable linker, and each dendrimer was modified with multiple mass tags via a photo-cleavable linker. In BLA detection, BLA could cleave the BLA-cleavable linker, leading to dendrimers shedding from the MP-CMSA probe to achieve enzyme-assisted signal amplification. Then, each dendrimer can further release mass tags under UV light to achieve light-assisted signal amplification. After this cascaded signal amplification, the released mass tags were ultimately quantified by mass spectrometry. Consequently, the sensitivity of BLA detection can be significantly enhanced by four orders of magnitude with a detection limit of 50.0 fM. Finally, this approach was applied to the blood samples from patients with DRB. This platform provides a potential strategy for the sensitive, rapid and quantitative detection of DRB infection.

Recent Progress on Solid Substrates for Surface-Enhanced Raman Spectroscopy Analysis

Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique with distinguished features of non-destructivity, ultra-sensitivity, rapidity, and fingerprint characteristics for analysis and sensors. The SERS signals are mainly dependent on the engineering of high-quality substrates. Recently, solid SERS substrates with diverse forms have been attracting increasing attention due to their promising features, including dense hot spot, high stability, controllable morphology, and convenient portability. Here, we comprehensively review the recent advances made in the field of solid SERS substrates, including their common fabrication methods, basic categories, main features, and representative applications, respectively. Firstly, the main categories of solid SERS substrates, mainly including membrane substrate, self-assembled substrate, chip substrate, magnetic solid substrate, and other solid substrate, are introduced in detail, as well as corresponding construction strategies and main features. Secondly, the typical applications of solid SERS substrates in bio-analysis, food safety analysis, environment analysis, and other analyses are briefly reviewed. Finally, the challenges and perspectives of solid SERS substrates, including analytical performance improvement and largescale production level enhancement, are proposed.

Ultrasensitive Sandwich-Type SERS-Biosensor-Based Dual Plasmonic Superstructure for Detection of Tacrolimus in Patients

Tacrolimus (FK506) is widely used in the prevention of organ transplant rejection and the treatment of autoimmune diseases, but it is difficult to detect within the low and narrow concentration range in practical clinical fields. A magnetic plasmonic superstructure-targets-plasmonic superstructure-based sandwich-type SERS biosensor is presented here to ultrasensitively detect FK506 in the blood of organ transplant patients. The spiky Fe₃O₄@SiO₂@Ag flower magnetic superstructure and hollow Ag@Au superstructure enhanced the SERS signals by providing rich sharp tips, cavities, and abundant hot spot gaps. And the magnetic feature makes it easy to concentrate and separate the biological target. Using the designed sandwich-type SERS biosensor, FK506 could be detected within a range of 0.5-20 ng/mL with a detection limit of 0.33 ng/mL. All results indicated that the sandwich-type SERS biosensor has good stability, sensitivity, and anti-interference properties. It is noteworthy that this allowed us to successfully analyze FK506 in the blood of transplant patients, which is in strong agreement with the clinical results. Consequently, the attractive sandwich-type SERS biosensor can be used for the detection of FK506 in real samples, which is promising for clinical diagnosis.

How Surface-Enhanced Raman Spectroscopy Could Contribute to Medical Diagnoses

In the last decade, there has been a rapid increase in the number of surface-enhanced Raman scattering (SERS) spectroscopy applications in medical research. In this article we review some recent, and in our opinion, most interesting and promising applications of SERS spectroscopy in medical diagnostics, including those that permit multiplexing within the range important for clinical samples. We focus on the SERS-based detection of markers of various diseases (or those whose presence significantly increases the chance of developing a given disease), and on drug monitoring. We present selected examples of the SERS detection of particular fragments of DNA or RNA, or of bacteria, viruses, and disease-related proteins. We also describe a very promising and elegant ‘lab-on-chip’ approach used to carry out practical SERS measurements via a pad whose action is similar to that of a pregnancy test. The fundamental theoretical background of SERS spectroscopy, which should allow a better understanding of the operation of the sensors described, is also briefly outlined. We hope that this review article will be useful for researchers planning to enter this fascinating field.

Etched-spiky Au@Ag plasmonic-superstructure monolayer films for triple amplification of surface-enhanced Raman scattering signals

Generally, a high quality surface-enhanced Raman spectroscopy (SERS) substrate often requires a highly-tailorable electromagnetic (EM) field generated at nanoparticle (NP) surfaces by the regulation of the morphologies, components and roughness of NPs. However, most recent universal approaches are restricted to single components, and integrating these key factors into one system to achieve the theoretically maximum signal amplification is still challenging. Herein, we design a triple SERS signal amplification platform by the coordination of spiky Au NPs with rich-tip nanostructures, controllable silver nanoshell, as well as tailorable surface roughness into one nano-system. As a result, the theoretical electromagnetic field of the interfacial self-assembled 2D substrate can be improved by nearly 5 orders of magnitude, and the ideal tracing capability for the model SERS molecule can be achieved at levels of 5 × 10^-11 M. Finally, diverse analytes in pesticide residues, environmental pollutants as well as medically diagnose down to 10^-11 M and can be fingerprinted by the proposed SERS nano-platform. Our integrated triple amplification platform not only provides an effective SERS sensing strategy, but also makes it possible to simultaneously achieve high sensitivity, stability as well as universality into one plasmonic-based SERS sensing system.

Serum fingerprinting by slippery liquid-infused porous SERS for non-invasive lung cancer detection

Direct and label-free analysis of clinical serum samples using slippery liquid-infused porous-enhanced Raman spectroscopy (SLIPSERS) enables the rapid non-invasive identification of lung cancer.

Reusable and universal impedimetric sensing platform for the rapid and sensitive detection of pathogenic bacteria based on bacteria-imprinted polythiophene film

A bacteria-imprinted polythiophene film (BIF)-based impedimetric sensor was proposed for the rapid and sensitive detection of S. aureus. A significant improvement is the reduced time for both BIF fabrication (15 min) and bacterial capturing (10 min).