A multifunctional SERS sticky note for real-time quorum sensing tracing and inactivation of bacterial biofilms

Wearable, Biocompatible, and Dual-Emission Ocular Multisensor Patch for Continuous Profiling of Fluoroquinolone Antibiotics in Tears

The abuse or misuse of antibiotics in clinical and agricultural settings severely endangers human health and ecosystems, which has raised profound concerns for public health worldwide. Trace detection and reliable discrimination of commonly used fluoroquinolone (FQ) antibiotics and their analogues have consequently become urgent to guide the rational use of antibiotic medicines and deliver efficient treatments for associated diseases. Herein, we report a wearable eye patch integrated with a quadruplex nanosensor chip for noninvasive detection and discrimination of primary FQ antibiotics in tears during routine eyedrop treatment. A set of dual-mode fluorescent nanoprobes of red- or green-emitting CdTe quantum dots integrated with lanthanide ions and a sensitizer, adenosine monophosphate, were constructed to provide an enhanced fluorescence up to 45-fold and nanomolar sensitivity toward major FQs owing to the aggregation-regulated antenna effect. The aggregation-driven, CdTe-Ln(III)-based microfluidic sensor chip is highly specific to FQ antibiotics against other non-FQ counterparts or biomolecular interfering species and is able to accurately discriminate nine types of FQ or non-FQ eyedrop suspensions using linear discriminant analysis. The prototyped wearable sensing detector has proven to be biocompatible and nontoxic to human tissues, which integrates the entire optical imaging modules into a miniaturized, smartphone-based platform for field use and reduces the overall assay time to ∼5 min. The practicability of the wearable eye patch was demonstrated through accurate quantification of antibiotics in a bactericidal event and the continuous profiling of FQ residues in tears after using a typical prescription antibiotic eyedrop. This technology provides a useful supplement to the toolbox for on-site and real-time examination and regulation of inappropriate daily drug use that might potentially lead to long-term antibiotic abuse and has great implications in advancing personal healthcare techniques for the regulation of daily medication therapy.

Surface-enhanced Raman scattering sensing for detection and mapping of key cellular biomarkers

Cellular biomarkers mainly contain proteins, nucleic acids, glycans and many small molecules including small biomolecule metabolites, reactive oxygen species and other cellular chemical entities. The detection and mapping of the key cellular biomarkers can effectively help us to understand important cellular mechanisms associated with physiological and pathological processes, which greatly promote the development of clinical diagnosis and disease treatment. Surface-enhanced Raman scattering (SERS) possesses high sensitivity and is free from the influence of strong self-fluorescence in living systems as well as the photobleaching of the dyes. It exhibits rich and narrow chemical fingerprint spectra for multiplexed detection, and has become a powerful tool to detect and map cellular biomarkers. In this review, we present an overview of recent advances in the detection and mapping of different classes of cellular biomarkers based on SERS sensing. These advances fully confirm that the SERS-based sensors and sensing methods have great potential for the exploration of biological mechanisms and clinical applications. Additionally, we also discuss the limitations of present research and the future developments of the SERS technology in this field.

Metabolite-Mediated Bacterial Antibiotic Resistance Revealed by Surface-Enhanced Raman Spectroscopy

A prompt on-site, real-time method to detect bacterial antibiotic resistance is crucial for controlling the spread of resistance. Herein, we report the use of surface-enhanced Raman spectroscopy (SERS) for the monitoring of bioactive metabolites produced by ampicillin-resistant Pseudomonas aeruginosa strains and identification of mechanisms underlying antibiotic resistance. The results indicate that the blue-green pigment pyocyanin (PYO) dominates the metabolite signals and is significantly enhanced upon exposure to subminimal inhibitory concentrations of ampicillin. PYO accumulates during exponential growth and subsequently either diffuses into the culture medium or is consumed in response to nutrient deprivation. The SERS spectra further reveal that the production of some intermediate substances such as polysaccharides and amino acids is minimally impacted and that nutrient consumption remains consistent. Moreover, the intensity changes and peak shifts observed in the SERS spectra of non-PYO-producing ampicillin-susceptible Escherichia coli demonstrate that exogenously added PYO enhances E. coli tolerance to ampicillin to some extent. These results indicate that PYO mediates antibiotic resistance not only in the parent species but also in cocultured bacterial strains. The metabolic SERS signal provides new insight regarding antibiotic resistance with promising applications for both environmental monitoring and rapid clinical detection.

Fabrication of flexible SERS substrate based on Au nanostars and PDMS for sensitive detection of Thiram residue in apple juice

We developed a novel fabrication of flexible surface-enhanced Raman scattering (SERS) substrate to perform selective and sensitive determination of thiram residue in fruits and juices. Au nanostars (Au NSs) with multi-branching structure were self-assembled on aminated Polydimethylsiloxane (PDMS) slides by electrostatic interaction. By measuring the Thiram's characteristic peak intensity at 1371 cm^-1, the SERS method could distinguish Thiram from other pesticide residues. A good linear relationship between the peak intensity at 1371 cm^-1 and thiram's concentration was established at the range from 0.01 ppm to 100 ppm and the Limit of detection is 0.0048 ppm. We directly used this SERS substrate to detect Thiram in apple juice. By standard addition method, recoveries varied in the range of 97.05% to 106.00% and the RSD were from 3.26% to 9.35%. The SERS substrate exhibited a good sensitivity, stability and selectively for the detection of Thiram in food samples, which can be spread as a common method for the detection of pesticides in food samples.

In Situ Spatiotemporal SERS Measurements and Multivariate Analysis of Virally Infected Bacterial Biofilms Using Nanolaminated Plasmonic Crystals

In situ spatiotemporal biochemical characterization of the activity of living multicellular biofilms under external stimuli remains a significant challenge. Surface-enhanced Raman spectroscopy (SERS), combining the molecular fingerprint specificity of vibrational spectroscopy with the hotspot sensitivity of plasmonic nanostructures, has emerged as a promising noninvasive bioanalysis technique for living systems. However, most SERS devices do not allow reliable long-term spatiotemporal SERS measurements of multicellular systems because of challenges in producing spatially uniform and mechanically stable SERS hotspot arrays to interface with large cellular networks. Furthermore, very few studies have been conducted for multivariable analysis of spatiotemporal SERS datasets to extract spatially and temporally correlated biological information from multicellular systems. Here, we demonstrate in situ label-free spatiotemporal SERS measurements and multivariate analysis of Pseudomonas syringae biofilms during development and upon infection by bacteriophage virus Phi6 by employing nanolaminate plasmonic crystal SERS devices to interface mechanically stable, uniform, and spatially dense hotspot arrays with the P. syringae biofilms. We exploited unsupervised multivariate machine learning methods, including principal component analysis (PCA) and hierarchical cluster analysis (HCA), to resolve the spatiotemporal evolution and Phi6 dose-dependent changes of major Raman peaks originating from biochemical components in P. syringae biofilms, including cellular components, extracellular polymeric substances (EPS), metabolite molecules, and cell lysate-enriched extracellular media. We then employed supervised multivariate analysis using linear discriminant analysis (LDA) for the multiclass classification of Phi6 dose-dependent biofilm responses, demonstrating the potential for viral infection diagnosis. We envision extending the in situ spatiotemporal SERS method to monitor dynamic, heterogeneous interactions between viruses and bacterial networks for applications such as phage-based anti-biofilm therapy development and continuous pathogenic virus detection.

Trimer structures formed by target-triggered AuNPs self-assembly inducing electromagnetic hot spots for SERS-fluorescence dual-signal detection of intracellular miRNAs

Accurate quantitative, in situ and temporal tracking imaging of tumor-associated miRNAs in living cells could provide a basis for cancer diagnosis and prognosis. In this strategy, a surface-enhanced Raman scattering (SERS)-fluorescence (FL) dual-spectral sensor (DSS) was constructed based on the nanoscale photophysical properties of AuNPs, mediated by functionalized DNA, to achieve rapid imaging of FL and accurate SERS quantification of intracellular miRNAs. The dual-spectrum sensor in the strategy is highly sensitive, specific and reproducibly stable. The LOD values of the dual spectra were 3.58 pM (SERS) as well as 11.8 pM (FL) with RSD values less than 2.69%. The bispectral sensor self-assembled into a trimer by the lapidation of Y-type DNA under the excitation of the target, generating a stable enhanced electric field coupling; and selected adenine located in the enhanced electric field as the reporter molecule, simplifying the labeling process and variables of the Raman reporter molecule, distinguishing it from other traditional methods. This strategy successfully achieved accurate tracking and quantification of miR-21 in cancer cells and showed good stability in the cells. The reported probes are potential tools for reliable monitoring of biomolecular dynamics in living cells.

Self-assembly of Au nanocrystals into large-area 3-D ordered flexible superlattice nanostructures arrays for ultrasensitive trace multi-hazard detection

Plasmonic nanoparticles that self-assemble into highly ordered superlattice nanostructures hold substantial promise for facilitating ultra-trace surface-enhanced Raman scattering (SERS) detection. Herein, we propose a boiling-point evaporation method to synthesize ordered monocrystal-like superlattice Au nanostructures (OML-Au NTs) with a polyhedral morphology. Combined with thermal nanoimprint technology, OML-Au NTs were directly transferred to impact-resistant polystyrene (IPS) flexible SERS substrates, the obtained flexible substrates (donated as OML-Au NTs/IPS) detection limit for R6G molecules as low as 10^-13 M. These results were confirmed by simulating the electromagnetic field distribution of ordered/unordered two-dimensional single-layer and three-dimensional aggregated gold nanostructures. The OML-Au NTs/IPS substrates were successfully used to detect and quantify three commonly-used agricultural pesticides, achieving detection limits as low as 10^-11 M and 10^-12 M, and in situ real-time detection limit reached 0.24 pg/cm² for thiram on apple peels, which was 3 orders of magnitude lower than the current detection limit. In addition, the Raman intensity from multiple locations showed a relative standard deviation lower than 7 %, exhibiting the reliability necessary for practical applications. As a result, this research demonstrates a highly reproducible method to enable the development of plasmonic nanomaterials with flexible superstructures.

Nanomaterials meet surface-enhanced Raman scattering towards enhanced clinical diagnosis: a review

Surface-enhanced Raman scattering (SERS) is a very promising tool for the direct detection of biomarkers for the diagnosis of i.e., cancer and pathogens. Yet, current SERS strategies are hampered by non-specific interactions with co-existing substances in the biological matrices and the difficulties of obtaining molecular fingerprint information from the complex vibrational spectrum. Raman signal enhancement is necessary, along with convenient surface modification and machine-based learning to address the former issues. This review aims to describe recent advances and prospects in SERS-based approaches for cancer and pathogens diagnosis. First, direct SERS strategies for key biomarker sensing, including the use of substrates such as plasmonic, semiconductor structures, and 3D order nanostructures for signal enhancement will be discussed. Secondly, we will illustrate recent advances for indirect diagnosis using active nanomaterials, Raman reporters, and specific capture elements as SERS tags. Thirdly, critical challenges for translating the potential of the SERS sensing techniques into clinical applications via machine learning and portable instrumentation will be described. The unique nature and integrated sensing capabilities of SERS provide great promise for early cancer diagnosis or fast pathogens detection, reducing sanitary costs but most importantly allowing disease prevention and decreasing mortality rates.

Surface-enhanced Raman spectroscopy enabled evaluation of bacterial inactivation

An improved understanding of bacterial inactivation mechanisms will provide useful insights for infectious disease control and prevention. We evaluated bacterial response to several inactivation methods using surface-enhanced Raman spectroscopy (SERS). The results indicate that changes in the SERS signal are highly related to cellular disruption and that cellular changes arising after cell inactivation cannot be ignored. The membrane integrity of heat and the combination of UV₂₅₄ and free chlorine (UV₂₅₄/chlorine) treated Pseudomonas syringae (P. syringae) cells were severely disrupted, leading to significantly increased peak intensities. Conversely, ethanol treated bacteria exhibited intact cell morphologies and the SERS spectra remained virtually unchanged. On the basis of time dependent SERS signals, we extracted dominant SERS patterns. Peaks related to nucleic acids accounted for the main changes observed during heat, UV₂₅₄, and UV₂₅₄/chlorine treatment, likely due to their outward diffusion from the cell cytoplasm. For free chlorine treated P. syringae, carbohydrates and proteins on the cell membrane were denatured or lost, resulting in a decrease in related peak intensities. The nucleobases were likely oxidized when treated with UV₂₅₄ and chlorine, thus leading to shifts in the related peaks. The generality of the method was verified using two additional bacterial strains: Escherichia coli and Bacillus subtilis as well as in different water matrices. The results suggest that SERS spectral analysis is a promising means to examine bacterial stress response at the molecular level and has applicability in diverse environmental implementations.

Cross-Wavelength Hierarchical Metamaterials Enabled for Trans-Scale Molecules Detection Simultaneously

Metamaterials have attracted increasing attention in sensing applications. However, the critical feature sizes of meta-atom span several orders of magnitude in length scale, almost all the metamaterials are designed to operate at limited bands. It is challenging for a single type of meta-atom with ultra-broadband adaptability. Inspired by the natural hierarchical architectures, herein, the authors introduce a new constructing scheme of cross-wavelength hierarchical metamaterials with a single type of meta-atom that can realize enhancement of terahertz (THz) resonance and surface-enhanced Raman scattering (SERS) at the same time. By combining multiple subwavelength structures at different hierarchical levels into a single meta-atom, the obtained metamaterial can operate in two frequencies and realize multiple functionalities. Armed with this hierarchical metamaterial, detecting analytes as small as sub-nanoscale chemical molecules or as big as microscale biomolecules simultaneously can be realized in one single metamaterial for the first time. As a proof-of-concept example, a smart sensory packaging is developed, which allowed them to real-time monitor the kinetic growth of pathogenic bacteria and their metabolites in food without opening the packaging. They believe that their work will provide a valuable example that satisfies the unmet need for multiscale functional meta-devices.

Highly sensitive SERS substrates with multi-hot spots for on-site detection of pesticide residues

Pesticide residues will be a huge threat to food security and ecological environment; therefore, there is an urgent need to achieve rapid and on-site detection of pesticide residues. Herein, a plasmonic substrate with multiple "hot spots" was fabricated by transferring three-dimensional (3D) Au nanoparticles (NPs) onto the polydimethylsiloxane (PDMS) membrane for highly sensitive surface-enhanced Raman scattering (SERS) detection of pesticide residues. In combination with 3D-FDTD simulations, high SERS enhancement (EF = 1.2 × 10⁸) and high detection sensitivity (LOD = 6.3 × 10^-10 M) were achieved, mainly due to the enhanced electromagnetic fields around the "hot spots". Additionally, the PDMS-based SERS substrate held good transparency and flexibility, enabling conformal contact with non-planar surfaces and allowing the laser to penetrate the back of the analytes. Combined with a portable Raman spectrometer, the substrates holds great potential for rapid, high-sensitive, and on-site detection of contaminants in food, especially for the analyte on the nonplanar surfaces.

Advanced detection and sensing strategies of Pseudomonas aeruginosa and quorum sensing biomarkers: A review

Pseudomonas aeruginosa (P. aeruginosa), a ubiquitous opportunistic pathogen, can frequently cause chronic obstructive pulmonary disease, cystic fibrosis and chronic wounds, and potentially lead to severe morbidity and mortality. Timely and adequate treatment of nosocomial infection in clinic depends on rapid detection and accurate identification of P. aeruginosa and its early-stage antibiotic susceptibility test. Traditional methods like plating culture, polymerase chain reaction, and enzyme-linked immune sorbent assays are time-consuming and require expensive equipment, limiting the rapid diagnostic application. Advanced sensing strategy capable of fast, sensitive and simple detection with low cost has therefore become highly desired in point of care testing (POCT) of nosocomial pathogens. Within this review, advanced detection and sensing strategies for P. aeruginosa cells along with associated quorum sensing (QS) molecules over the last ten years are discussed and summarized. Firstly, the principles of four commonly used sensing strategies including localized surface plasmon resonance (LSPR), surface-enhanced Raman spectroscopy (SERS), electrochemistry, and fluorescence are briefly overviewed. Then, the advancement of the above sensing techniques for P. aeruginosa cells and its QS biomarkers detection are introduced, respectively. In addition, the integration with novel compatible platforms towards clinical application is highlighted in each section. Finally, the current achievements are summarized along with proposed challenges and prospects.

Surface-Enhanced Raman Spectroscopy of Bacterial Metabolites for Bacterial Growth Monitoring and Diagnosis of Viral Infection

Bacterial metabolites are intermediate products of bacterial metabolism and their production reflects metabolic activity. Herein, we report the use of surface-enhanced Raman spectroscopy (SERS) for detection of both volatile and nonvolatile metabolites and the application of this approach for bacterial growth quantification and diagnosis of viral infection. The time-dependent SERS signal of the volatile metabolite dimethyl disulfide in the headspace above bacteria growing on an agar plate was detected and quantified. In addition, SERS signals arising from the plate reflected nutrient consumption and production of nonvolatile metabolites. The measurement of metabolite accumulation can be used for bacterial quantification. In the presence of bacteriophage virus, bacterial metabolism is suppressed, and the relative decrease in SERS intensity reflects the initial virus concentration. Using multivariate analysis, we detect viral infection with a prediction accuracy of 93%. Our SERS-based approach for metabolite production monitoring provides new insights toward viral infection diagnosis.

Gold Nanomaterials as a Promising Integrated Tool for Diagnosis and Treatment of Pathogenic Infections-A Review

This review summarizes research on functionalized gold nanomaterials as pathogen detection sensors and pathogen elimination integrated tools. After presenting the challenge of current severe threat from pathogenic bacteria and the increasingly serious growth rate of drug resistance, the first section mainly introduces the conspectus of gold nanostructures from synthesis, characterization, physicochemical properties and applications of gold nanomaterials. The next section deals with gold nanomaterials-based pathogen detection sensors such as colorimetric sensors, fluorescence sensors and Surface-Enhanced Raman Scattering sensors. We then discuss strategies based on gold nanomaterials for eliminating pathogenic infections, such as the dual sterilization strategy for grafting gold nanomaterials with antibacterial substances, photothermal antibacterial and photodynamic antibacterial methods. The fourth part briefly introduces the comprehensive strategy for diagnosis and sterilization of pathogen infection based on gold nanomaterials, such as the diagnosis and treatment strategy for pathogen infection using Roman signals real-time monitoring and photothermal sterilization. A concluding section that summarizes the current status and challenges of the novel diagnosis and treatment integrated strategy for pathogenic infections, gives an outlook on potential future perspectives.

Photo-responsive functional gold nanocapsules for inactivation of community-acquired, highly virulent, multidrug-resistant MRSA

The indiscriminate and sporadic use of antibiotics has contributed to the emergence of drug resistance phenomenon in bacteria including but not limited to Staphylococcus aureus. These drug-resistant bacteria have been threatening safety in hospitals and adversely affecting human health. Here we report a strategy to design photo-stimulated theranostic nanoprobes against methicillin-resistant Staphylococcus aureus (MRSA) "superbug" USA300. The nanocapsule probe is based on gold nanorods (GNRs) coated with pegylated thiol, mPEG-SH, which has been further modified by adding successively a natural antibacterial compound such as curcumin, and a cell targeting deoxyribonucleic acid (DNA) aptamer. We have used this novel gold nanocapsules for near-infrared (NIR) photophysical stimulation against pathogenic bacteria. We have found that the novel nanocapsule blocks biofilm formation and kills bacteria by photothermal action that causes disruption of the bacterial cell wall and membrane. In this approach, multiple drug-resistant Staphylococcus aureus has been captured by these nanocapsules through DNA aptamer targeting. All of the trapped bacteria could be killed in 30 minutes during the NIR stimulation due to the combination of photothermal effect, the generation of reactive oxygen species (ROS) and a loss of transmembrane potential (Δψ). Importantly we did not notice any resistance developed against the photothermal treatment. This is remarkable from an anti-biofilm activity point of view. Importantly, these multifunctional nanocapsules have also shown a surface enhanced Raman spectroscopy (SERS) effect, which could be used to evaluate the success of the inactivation effect during treatment. These results indicate that nanocapsule-based photo treatment can be an alternative antibacterial strategy without contributing to antibiotic resistance, and thus can be used for both environmental and therapeutic applications.

A photo-sensitizable phage for multidrug-resistant Acinetobacter baumannii therapy and biofilm ablation

Antibiotic abuse causes the emergence of bacterial resistance. Photodynamic antibacterial chemotherapy (PACT) has great potential to solve serious bacterial resistance, but it suffers from the inefficient generation of ROS and the lack of bacterial targeting ability. Herein, a unique cationic photosensitizer (NB) and bacteriophage (ABP)-based photodynamic antimicrobial agent (APNB) is developed for precise bacterial eradication and efficient biofilm ablation. Thanks to the structural modification of the NB photosensitizer with a sulfur atom, it displays excellent reactive oxygen species (ROS)-production ability. Moreover, specific binding to pathogenic microorganisms can be provided by bacteriophages. The developed APNB has multiple functions, including bacteria targeting, near-infrared fluorescence imaging and combination therapy (PACT and phage therapy). Both in vitro and in vivo experiments prove that APNB can efficiently treat A. baumannii infection. Particularly, the recovery from A. baumannii infection after APNB treatment is faster than that with ampicillin and polymyxin B in vivo. Furthermore, the strategy of combining bacteriophages and photosensitizers is employed to eradicate bacterial biofilms for the first time, and it shows the excellent biofilm ablation effect as expected. Thus, APNB has huge potential in fighting against multidrug-resistant bacteria and biofilm ablation in practice.

APNB for multidrug-resistant A. Baumannii therapy and biofilms ablation.

Optical nanosensors for biofilm detection in the food industry: principles, applications and challenges

Biofilms are the universal lifestyle of bacteria enclosed in extracellular polymeric substances (EPS) on the contact surfaces of food processing facilities. The EPS-encapsulated foodborne bacterial pathogens are the main food contaminant sources, posing a serious threat to human health. The microcrystalline, sophisticated and dynamic biofilms necessitate the development of conventional microscopic imaging and spectral technology. Nanosensors, which can transfer the biochemical information into optical signals, have recently emerged for biofilm optical detection with high sensitivity and high spatial resolution at nanoscale scopes. Therefore, the aim of this review is to clarify the main detection scope in biofilms and the detection principles of optical nanosensors arousing Raman enhancement, fluoresce conversion and color change. The difficulties and challenges of biofilm characterization including the secretion and variation of main biochemical components are first discussed, the details about the principles and application examples of bioassays targeting foodborne pathogens based on optical nanosensors are then summarized. Finally, the challenges and future trends in developing optical nanosensors are also highlighted. The current review indicates that optical nanosensors have taken the challenges of detecting biofilm in complex food samples, including the characterization of biofilm formation mechanism, identification of microbial metabolic activities, diagnosis of potential food pathogens and sanitation monitoring of food processing equipment. Numerous in-depth explorations and various trials have proven that the bioassays based on multifunctional optical nanosensors are promising to ensure and promote food safety and quality. However, there still remains a daunting challenge to structure reproducible, biocompatible and applicable nano-sensors for biofilm characterization, identification, and imaging.

Nanoparticle-Based Wound Dressing: Recent Progress in the Detection and Therapy of Bacterial Infections

Bacterial infections in wounds often delay the healing process, and may seriously threaten human life. It is urgent to develop wound dressings to effectively detect and treat bacterial infections. Nanoparticles have been extensively used in wound dressings because of their specific properties. This review highlights the recent progress on nanoparticle-based wound dressings for bacterial detection and therapy. Specifically, nanoparticles have been applied as intrinsic antibacterial agents or drug delivery vehicles to treat bacteria in wounds. Moreover, nanoparticles with photothermal or photodynamic property have also been explored to endow wound dressings with significant optical properties to further enhance their bactericidal effect. More interestingly, nanoparticle-based smart dressings have been recently explored for bacteria detection and treatment, which enables an accurate assessment of bacterial infection and a more precise control of on-demand therapy.

A Biomimetic Plasmonic Nanoreactor for Reliable Metabolite Detection

Reliable monitoring of metabolites in biofluids is critical for diagnosis, treatment, and long-term management of various diseases. Although widely used, existing enzymatic metabolite assays face challenges in clinical practice primarily due to the susceptibility of enzyme activity to external conditions and the low sensitivity of sensing strategies. Inspired by the micro/nanoscale confined catalytic environment in living cells, the coencapsulation of oxidoreductase and metal nanoparticles within the nanopores of macroporous silica foams to fabricate all-in-one bio-nanoreactors is reported herein for use in surface-enhanced Raman scattering (SERS)-based metabolic assays. The enhancement of catalytical activity and stability of enzyme against high temperatures, long-time storage or proteolytic agents are demonstrated. The nanoreactors recognize and catalyze oxidation of the metabolite, and provide ratiometric SERS response in the presence of the enzymatic by-product H2O2, enabling sensitive metabolite quantification in a "sample in and answer out" manner. The nanoreactor makes any oxidoreductase-responsible metabolite a candidate for quantitative SERS sensing, as shown for glucose and lactate. Glucose levels of patients with bacterial infection are accurately analyzed with only 20 µL of cerebrospinal fluids, indicating the potential application of the nanoreactor in vitro clinical testing.

Dual bioresponsive antibiotic and quorum sensing inhibitor combination nanoparticles for treatment of Pseudomonas aeruginosa biofilms in vitro and ex vivo

Many debilitating infections result from persistent microbial biofilms that do not respond to conventional antibiotic regimens. A potential method to treat such chronic infections is to combine agents which interfere with bacterial biofilm development together with an antibiotic in a single formulation. Here, we explore the use of a new bioresponsive polymer formulation derived from specifically modified alginate nanoparticles (NPs) in order to deliver ciprofloxacin (CIP) in combination with the quorum sensing inhibitor (QSI) 3-amino-7-chloro-2-nonylquinazolin-4(3H)-one (ACNQ) to mature Pseudomonas aeruginosa biofilms. The alginate NPs were engineered to incorporate a pH-responsive linker between the polysaccharide backbone and the QSI, and to encapsulate CIP via charge-charge interactions of the positively-charged drug with the carboxyl residues of the alginate matrix. In this way, a dual-action release of antibiotic and QSI was designed for the low-pH regions of a biofilm, involving cleavage of the QSI-linker to the alginate matrix and reduced charge-charge interactions between CIP and the polysaccharide as the alginate carboxyl side-chains protonated. When tested in a biofilm model the concomitant release of CIP + QSI from the pH-responsive nanoparticles significantly reduced the viability of the biofilm compared with CIP treatment alone. In addition, the alginate NPs were shown to penetrate deeply into P. aeruginosa biofilms, which we attribute in part to the charges of the NPs and the release of the QSI agent. Finally, we tested the formulation in both a 2D keratinocyte and a 3D ex vivo skin infection model. The dual-action bio-responsive QSI and CIP release nanoparticles effectively cleared the infection in the latter, suggesting considerable promise for combination therapeutics which prevent biofilm formation as well as effectively killing mature P. aeruginosa biofilms.

A Filter Supported Surface-Enhanced Raman Scattering "Nose" for Point-of-Care Monitoring of Gaseous Metabolites of Bacteria

This work designs a convenient method for fabrication of surface-enhanced Raman scattering (SERS) devices by loading gold nanostars (AuNSs) on a flat filter support with vacuum filtration. The dense accumulation of AuNSs results in a strong sensitization to SERS signal and shows sensitive response to gaseous metabolites of bacteria, which produces a SERS "nose" for rapid point-of-care monitoring of these metabolites. The "nose" shows good reproducibility and stability and can be used for SERS quantitation of a gaseous target with Raman signal. The impressive performance of the proposed SERS "nose" for detecting gaseous metabolites of common foodborne bacteria like Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa from inoculated samples demonstrates its much higher sensitivity than that of human sense and application in distinguishing spoiled food at an early stage and real-time tracing of food spoilage degree. The strong point-of-care testing ability of the designed SERS "nose" and the miniaturization of whole equipment extend greatly the analytical application of SERS technology in food safety and public health.

"Three-in-One" SERS Adhesive Tape for Rapid Sampling, Release, and Detection of Wound Infectious Pathogens

The traditional colony culture method for detection of pathogens is subjected to the laborious and tedious experimental procedure, which limits its application in point-of-care (POC) testing and quick diagnosis. This work designs an intelligent adhesive tape as a "three-in-one" platform for rapid sampling, photocontrolled release, and surface-enhanced Raman scattering (SERS) detection of pathogens from infected wounds. This tape is constructed by encapsulating densely packed gold nanostars as SERS substrates between two pieces of graphene and modified with a synthetic o-nitrobenzyl derivative molecule to form an artificial biointerface for highly efficient pathogen capture via electrostatic interaction. The captured targets can be conveniently released onto a solid culture medium by UV cleavage of o-nitrobenzyl moiety for pathogen growth and in situ SERS detection. As a proof of strategy, this "three-in-one" platform has been used for detecting the concurrent infection of Pseudomonas aeruginosa and Staphylococcus aureus by pasting the tape on a skin burn wound. The impressive detection performance with an analytical time of only several hours for these pathogens at an early growth stage demonstrates its great potential as a POC testing device for health care.

Dual-Amplification Strategy-Based SERS Chip for Sensitive and Reproducible Detection of DNA Methyltransferase Activity in Human Serum

Herein, we present a dual-amplification sensing strategy-based surface-enhanced Raman scattering (SERS) chip, which combines rolling circle amplification (RCA) and polyadenine (PolyA) assembly for sensitive and reproducible determination of the activity of M.SssI, a cytosine-guanine dinucleotide (CpG) methyltransferase (MTase). Typically, in the presence of M.SssI, RCA process is triggered, resulting in long, single-stranded DNA (ssDNA) fragments that are hybridized with thousands of Raman reporters of Cy3. Afterward, the resultant ssDNA fragments are conjugated to SERS-active substrates made of silver core-gold satellite nanocomposites-modified silicon wafer (Ag-Au NPs@Si), with the SERS enhancement factor of ∼5 × 10⁶. The core-satellite nanostructures are assembled relied on the strong affinity of PolyA toward gold/silver surface. Of particular significance, the developed SERS chip displays an ultrahigh sensitivity with a low limit of detection (LOD) of 2.8 × 10^-3 U/mL, which is around 2 orders of magnitude higher than most reported methods. In addition, the constructed chip features a broad detection range covering from 0.05 to 50 U/mL. Besides for the ultrahigh sensitivity and broad dynamic range, the chip also features good reproducibility (e.g., the relative standard deviation (RSD) is less than ∼12%). Taking advantages of these merits, the developed chip is feasible for accurate discrimination of M.SssI with various concentrations spiked in human serum samples with good recoveries ranging from 99.6% to 107%.

Analysis of Biomolecules Based on the Surface Enhanced Raman Spectroscopy

Analyzing biomolecules is essential for disease diagnostics, food safety inspection, environmental monitoring and pharmaceutical development. Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for detecting biomolecules due to its high sensitivity, rapidness and specificity in identifying molecular structures. This review focuses on the SERS analysis of biomolecules originated from humans, animals, plants and microorganisms, combined with nanomaterials as SERS substrates and nanotags. Recent advances in SERS detection of target molecules were summarized with different detection strategies including label-free and label-mediated types. This comprehensive and critical summary of SERS analysis of biomolecules might help researchers from different scientific backgrounds spark new ideas and proposals.