SERS-based rapid susceptibility testing of commonly administered antibiotics on clinically important bacteria species directly from blood culture of bacteremia patients.

Bloodstream infections are a growing public health concern due to emerging pathogens and increasing antimicrobial resistance. Rapid antibiotic susceptibility testing (AST) is urgently needed for timely and optimized choice of antibiotics, but current methods require days to obtain results. Here, we present a general AST protocol based on surface-enhanced Raman scattering (SERS-AST) for bacteremia caused by eight clinically relevant Gram-positive and Gram-negative pathogens treated with seven commonly administered antibiotics. Our results show that the SERS-AST protocol achieves a high level of agreement (96% for Gram-positive and 97% for Gram-negative bacteria) with the widely deployed VITEK 2 diagnostic system. The protocol requires only five hours to complete per blood-culture sample, making it a rapid and effective alternative to conventional methods. Our findings provide a solid foundation for the SERS-AST protocol as a promising approach to optimize the choice of antibiotics for specific bacteremia patients. This novel protocol has the potential to improve patient outcomes and reduce the spread of antibiotic resistance.

Rapid detection of nicotine and benzoic acid in e-liquids with surface-enhanced Raman scattering and artificial intelligence-assisted spectrum interpretation.

Electronic cigarettes have rapidly gained acceptance recently. Nicotine-containing electronic cigarette liquids (e-liquids) are prohibited in some countries, but are permitted and simply available online in others. A rapid detection method is therefore required for on-site inspection or screening of a large amount of samples. Our previous study demonstrated a surface-enhanced Raman scattering (SERS)-based approach to identify nicotine-containing e-liquids; without any pre-treatment, e-liquid can be directly tested on our solid-phase SERS substrates, made of silver nanoparticle arrays embedded in anodic aluminium oxide nanochannels (Ag/AAO). However, this approach required manual determination of spectral signatures and negative samples should be validated in the second round detection. Here, after examining 406 commercial e-liquids, we refined this approach by developing artificial intelligence (AI)-assisted spectrum interpretations. We also found that nicotine and benzoic acid can be simultaneously detected in our platform. This increased test sensitivity because benzoic acid is usually used in nicotine salts. Around 64% of nicotine-positive samples in this study showed both signatures. Using either cutoffs of nicotine and benzoic acid peak intensities or a machine learning model based on the CatBoost algorithm, over 90% of tested samples can be correctly discriminated with only one round of SERS measurement. False negative and false positive rates were 2.5-4.4% and 4.4-8.9%, respectively, depending on the interpretation method and thresholds applied. The new approach takes only 1 microliter of sample and can be performed in 1-2 min, suitable for on-site inspection with portable Raman detectors. It could also be a complementary platform to reduce samples that need to be analyzed in the central labs and has the potential to identify other prohibited additives.

An antibiotic concentration gradient microfluidic device integrating surface-enhanced Raman spectroscopy for multiplex antimicrobial susceptibility testing.

Antimicrobial susceptibility testing (AST) is a key measure in clinical microbiology laboratories to enable appropriate antimicrobial administration. During an AST, the determination of the minimum inhibitory concentration (MIC) is an important step in which the bacterial responses to an antibiotic at a series of concentrations obtained in separate bacterial growth chambers or sites are compared. However, the preparation of different antibiotic concentrations is time-consuming and labor-intensive. In this paper, we present a microfluidic device that generates a concentration gradient for antibiotics that is produced by diffusion in the laminar flow regime along a series of lateral microwells to encapsulate bacteria for antibiotic treatment. All the AST preparation steps (including bacterium loading, antibiotic concentration generation, buffer washing, and isolated bacterial growth with an antibiotic) can be performed in a single chip. The viable bacterial cells in each microwell after the antibiotic treatment are then quantified by their surface-enhanced Raman scattering (SERS) signals that are acquired after placing a uniform SERS-active substrate in contact with all the microwells. For proof-of-concept, we demonstrated the AST performance of this system on ampicillin (AMP)-susceptible and -resistant E. coli strains. Compared with the parameters for conventional AST methods, the AST procedure based on this chip requires only 20 µL of bacteria solution and 5 h of operation time. This result indicates that this integrated system can greatly shorten and simplify the tedious and labor-intensive procedures required for current standard AST methods.

Nanometer-scaled landscape of polymer: fullerene blends mapped with visibles-SNOM.

Bulk heterojunction is one key concept leading to breakthrough in organic photovoltaics. The active layer is expectantly formed of distinct morphologies that carry out their respective roles in photovoltaic performance. The morphology-performance relationship however remains stymied, because unequivocal morphology at the nanoscale is not available. We used scattering-type scanning near-field optical microscopy operating with a visible light source (visibles-SNOM) to disclose the nanomorphology of P3HT:PCBM and pBCN:PCBM blends. Donor and acceptor domain as well as intermixed phase were identified and their intertwined distributions were mapped. We proposed energy landscapes of the BHJ active layer to shed light on the roles played by these morphologies in charge separation, transport and recombination. This study shows that visibles-SNOM is capable of profiling the morphological backdrop pertaining to the operation of high performance organic solar cells.

A microfluidic microwell device operated by the automated microfluidic control system for surface-enhanced Raman scattering-based antimicrobial susceptibility testing.

Bloodstream infection (BSI) is a serious public health issue worldwide. Timely and effective antibiotics for controlling infection are crucial towards patient outcomes. However, the current culture-based methods of identifying bacteria and antimicrobial susceptibility testing (AST) remain labor-intensive and time-consuming, and are unable to provide early support to physicians in critical hours. To improve the effectiveness of early antibiotic therapy, Surface-enhanced Raman scattering (SERS) technology, has been used in bacterial detection and AST based on its high specificity and label-free features. To simplify sample preparation steps in SERS-AST, we proposed an automated microfluidic control system to integrate all required procedures into a single device. Our preliminary results demonstrated the system can achieve on-chip reagent replacement, bacteria trapping, and buffer exchange. Finally, in-situ SERS-AST was performed within 3.5 h by loading isolates of ampicilin susceptible and resistant E. coli and clear discrimination of two strains under antibiotic treatment was demonstrated. Overall, our system can standardize and simplify the SERS-AST protocol and implicate parallel bacterial detection. This prototypical integration demonstrates timely microbiological support to optimize early antibiotic therapy for fighting bacteremia.

Speciation Analysis of Cr(VI) and Cr(III) in Water with Surface-Enhanced Raman Spectroscopy.

Identifying and quantifying chromium in water are important for the protection of precious water resources from chromium pollution. Standard methods however are unable to easily distinguish toxic hexavalent chromium, Cr(VI), from innocuous trivalent chromium, Cr(III), are time-consuming, or require large sample quantity. We show in this report that Cr(VI) and Cr(III) in water can be differentiated based on their distinct spectral features of surface-enhanced Raman scattering (SERS). Their SERS signals exhibit different pH dependences: the SERS features of Cr(VI) and Cr(III) are most prominent at pH values of 10 and 5.5, respectively. The obtained limit of detection of Cr(VI) in water is below 0.1 mg/L. Both concentration curves of their SERS signals show Langmuir sorption isotherm behavior. A procedure was developed to quantify Cr(VI) concentration based on the direct retrieval or addition method with an error of 10%. Finally, the SERS detection of Cr(VI) is shown to be insensitive to co-present Cr(III). The developed SERS procedure offers potential to monitor toxic chromium in fields.

Sensible Functional Linear Discriminant Analysis Effectively Discriminates Enhanced Raman Spectra of Mycobacterium Species.

Tuberculosis caused by Mycobacterium tuberculosis complex (MTBC) is one of the major infectious diseases in the world. Identification of MTBC and differential diagnosis of nontuberculous mycobacteria (NTM) species impose challenges because of their taxonomic similarity. This study describes a differential diagnosis method using the surface-enhanced Raman scattering (SERS) measurement of molecules released by Mycobacterium species. Conventional principal component analysis and linear discriminant analysis methods successfully separated the acquired spectrum of MTBC from those of NTM species but failed to distinguish between the spectra of different NTM species. A novel sensible functional linear discriminant analysis (SLDA), projecting the averaged spectrum of a bacterial specie to the subspace orthogonal to the within-species random variation, thereby eliminating its influence in applying linear discriminant analysis, was employed to effectively discriminate not only MTBC but also species of NTM. The successful demonstration of this SERS-SLDA method opens up new opportunities for the rapid differentiation of Mycobacterium species.

Rapid antibiotic susceptibility testing of bacteria from patients' blood via assaying bacterial metabolic response with surface-enhanced Raman spectroscopy.

Blood stream infection is one of the major public health issues characterized with high cost and high mortality. Timely effective antibiotics usage to control infection is crucial for patients' survival. The standard microbiological diagnosis of infection however can last days. The delay in accurate antibiotic therapy would lead to not only poor clinical outcomes, but also to a rise in antibiotic resistance due to widespread use of empirical broad-spectrum antibiotics. An important measure to tackle this problem is fast determination of bacterial antibiotic susceptibility to optimize antibiotic treatment. We show that a protocol based on surface-enhanced Raman spectroscopy can obtain consistent antibiotic susceptibility test results from clinical blood-culture samples within four hours. The characteristic spectral signatures of the obtained spectra of Staphylococcus aureus and Escherichia coli-prototypic Gram-positive and Gram-negative bacteria-became prominent after an effective pretreatment procedure removed strong interferences from blood constituents. Using them as the biomarkers of bacterial metabolic responses to antibiotics, the protocol reported the susceptibility profiles of tested drugs against these two bacteria acquired from patients' blood with high specificity, sensitivity and speed.

Bacteria encapsulation and rapid antibiotic susceptibility test using a microfluidic microwell device integrating surface-enhanced Raman scattering.

The antibiotic susceptibility test (AST) is a general laboratory procedure for bacterial identification and characterization and can be utilized to determine effective antimicrobials for individual patients. Due to the low bacterial concentration, conventional AST usually requires a prolonged bacterial culture time and a labor-intensive sample pretreatment process. Therefore, it cannot perform timely diagnosis or treatment, which results in a high mortality rate for seriously infected patients. To address this problem, we developed a microfluidic microwell device integrating surface-enhanced Raman scattering (SERS) technology, or the so called the Microwell-SERS system, to enable a rapid and high-throughput AST. Our results show that the Microwell-SERS system can successfully encapsulate bacteria in a miniaturized microwell with a greatly increased effective bacteria concentration, resulting in a shorter bacterial culture time. By attaching a microchannel onto the microwell, a smooth liquid and air exchange can purify the surrounding buffer and isolate bacteria in an individual microwell for independent SERS measurement. For proof-of-concept, we demonstrated a 2 h AST on susceptible and resistant E. coli and S. aureus with a concentration of 103 CFU mL-1 in the Microwell-SERS system, whereas the previous SERS-AST method required 108 CFU mL-1 bacterial suspension droplets dispensing on a SERS substrate. Based on the above features, we envision that the Microwell-SERS system could achieve highly sensitive, label-free, bacteria detection and rapid AST to enable timely and accurate bacterial infection disease diagnosis.

Rapid identification of nicotine in electronic cigarette liquids based on surface-enhanced Raman scattering.

Nicotine-containing electronic cigarette liquid (e-liquid) is prohibited in many countries, creating requirements for rapid detection approaches for on-site inspection or screening for large amounts of samples. Here, we demonstrate a simple way to identify nicotine using surface-enhanced Raman scattering (SERS) with substrates made of silver nanoparticle arrays imbedded in anodic aluminum oxide nanochannels (Ag/AAO). Compared with the reported colloidal nanoparticle-based SERS, that required serial dilutions to enable colloid aggregation in the viscous e-liquid, a small amount of undiluted e-liquid sample can be directly added onto our solid-phase Ag/AAO substrate without any pre-treatment. The sensitivity of our SERS measurements is 2-3 orders of magnitude higher than that required for identification of nicotine in e-liquid, which is typically around 1000-18,000 ppm. Using such nanoparticle array-based SERS, we have tested 22 commercially available e-liquid products, using the corresponding gas chromatography-mass spectrometry (GC-MS) reports as the reference. The SERS measurements were done within one hour and successfully identified 20 samples. Only 2 samples showed SERS interference from ingredients that were not suitable for SERS analysis.

Antibiotic Susceptibility Test with Surface-Enhanced Raman Scattering in a Microfluidic System.

Antibiotic susceptibility test (AST) is essential in clinical diagnosis of serious bacterial infection, such as sepsis, while it typically takes 2-5 days for sample culture, antibiotic treatment, and reading result. Detecting metabolites secreted from bacteria with surface-enhanced Raman scattering (SERS) enables rapid determination of antibiotic susceptibility, reducing the AST time to 1-2 days. However, it still requires 1 day of culture time to obtain sufficient quantity of bacteria for sample washing, bacterial extraction, and antibiotic treatment. Additionally, the whole procedure, manually performed in open environment, often suffers from contamination and human error. To address the above problems, a microfluidic system integrating membrane filtration and the SERS-active substrate (MF-SERS) was developed to perform on-chip bacterial enrichment, metabolite collection, and in situ SERS measurements for antibiotic susceptibility test. Using Escherichia coli as the prototype bacterium, the lowest SERS detection limit of bacterial concentration of the MF-SERS system is 103 CFU/mL, which is 4 orders of magnitude lower than that using centrifugation-purification procedure, significantly shortening the bacterial culture time. The bacteria and secreted metabolites are enclosed during bacterial trapping, metabolite filtration, and SERS detection, thus minimizing possible contamination and human errors. Finally, the successful demonstration of AST on E. coli with a concentration of 103 CFU/mL is presented. Overall, the MF-SERS system with a miniature size and well-confined microenvironment allows the integration of multiple bacteria processes for bacterial enrichment, culture, and determination of AST.

New D-A-A-Configured Small-Molecule Donors for High-Efficiency Vacuum-Processed Organic Photovoltaics under Ambient Light.

Four new donor-acceptor-acceptor (D-A-A) type molecules (DTCPB, DTCTB, DTCPBO, and DTCTBO), wherein benzothiadiazole or benzoxadiazole serves as the central A bridging triarylamine (D) and cyano group (terminal A), have been synthesized and characterized. The intramolecular charge-transfer character renders these molecules with strong visible light absorption and forms antiparallel dimeric crystal packing with evident π-π intermolecular interactions. The characteristics of the vacuum-processed photovoltaic device with a bulk heterojunction active layer employing these molecules as electronic donors combining C70 as electronic acceptor were examined and a clear structure-property-performance relationship was concluded. Among them, the DTCPB-based device delivers the best power conversion efficiency (PCE) up to 6.55% under AM 1.5 G irradiation. The study of PCE dependence on the light intensity indicates the DTCPB-based device exhibits superior exciton dissociation and less propensity of geminated recombination, which was further verified by a steady photoluminescence study. The DTCPB-based device was further optimized to give an improved PCE up to 6.96% with relatively high stability under AM 1.5 G continuous light-soaking for 150 h. This device can also perform a PCE close to 16% under a TLD-840 fluorescent lamp (800 lux), indicating its promising prospect for indoor photovoltaic application.

Quantification of biomolecules responsible for biomarkers in the surface-enhanced Raman spectra of bacteria using liquid chromatography-mass spectrometry.

Recently, specific biomarkers in the surface-enhanced Raman scattering (SERS) spectra of bacteria have been successfully exploited for rapid bacterial antibiotic susceptibility testing (AST) - dubbed SERS-AST. The biomolecules responsible for these bacterial SERS biomarkers have been identified as several purine derivative metabolites involved in bacterial purine salvage pathways (W. R. Premasiri, J. C. Lee, A. Sauer-Budge, R. Theberge, C. E. Costello and L. D. Ziegler, Anal. Bioanal. Chem., 2016, 408, 4631). Here we quantified these metabolites in the SERS spectra of Staphylococcus aureus and Escherichia coli using ultra-performance liquid chromatography/electrospray ionization-mass spectrometry (UPLC/ESI-MS). The time dependences of the concentrations of these molecules were measured using 13C- or 12C-purine derivatives as internal and external standards respectively in UPLC/ESI-MS measurements. Surprisingly, a single S. aureus and an E. coli cell were found to release millions of adenine and hypoxanthine into a water environment in an hour respectively. Furthermore, simulated SERS spectra of bacterial supernatants based on the mixtures of purine derivatives with measured concentrations also show great similarity with those of the corresponding bacterial samples. Our results not only provide a quantitative foundation for the emerging SERS-AST method but also suggest the potential of exploiting SERS for in situ monitoring the changes in bacterial purine salvage processes in response to different physical and chemical challenges.

SERS Detection of Biomolecules by Highly Sensitive and Reproducible Raman-Enhancing Nanoparticle Array.

This paper describes the preparation of nanoarrays composed of silver nanoparticles (AgNPs: 20-50 nm) for use as surface-enhanced Raman scattering (SERS) substrates. The AgNPs were grown on porous anodic aluminum oxide (AAO) templates by electrochemical plating, and the inter-channel gap of AAO channels is between 10 and 20 nm. The size and interparticle gap of silver particles were adjusted in order to achieve optimal SERS signals and characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. The fluctuation of SERS intensity is about 10-20% when measuring adenine solutions, showing a great reproducible SERS sensing. The nanoparticle arrays offer a large potential for practical applications as shown by the SERS-based quantitative detection and differentiation of adenine (A), thymine (T), cytosine (C), guanine (G), ß-carotene, and malachite green. The respective detection limits are <1 ppb for adenine and <0.63 ppm for ß-carotene and malachite green, respectively. Uniform and reproducible Raman enhancement enabled by Ag nanoparticle array embedded in anodic aluminum oxide differentiates and helps quantify DNA canonical nucleobases (adenine, thymine, cytosine, and guanine).

Ultrahigh Responsivity and Detectivity Graphene-Perovskite Hybrid Phototransistors by Sequential Vapor Deposition.

In this work, graphene-methylammonium lead iodide (MAPbI3) perovskite hybrid phototransistors fabricated by sequential vapor deposition are demonstrated. Ultrahigh responsivity of 1.73 × 107 A W-1 and detectivity of 2 × 1015 Jones are achieved, with extremely high effective quantum efficiencies of about 108% in the visible range (450-700 nm). This excellent performance is attributed to the ultra-flat perovskite films grown by vapor deposition on the graphene sheets. The hybrid structure of graphene covered with uniform perovskite has high exciton separation ability under light exposure, and thus efficiently generates photocurrents. This paper presents photoluminescence (PL) images along with statistical analysis used to study the photo-induced exciton behavior. Both uniform and dramatic PL intensity quenching has been observed over entire measured regions, consistently demonstrating excellent exciton separation in the devices.

Exciplex-Sensitized Triplet-Triplet Annihilation in Heterojunction Organic Thin-Film.

A new concept for organic light-emitting diodes (OLEDs) is presented, which is called exciplex-sensitized triplet-triplet annihilation (ESTTA). The exciplex formed at the organic heterojunction interface of 4,4',4″-tris(N-3-methyphenyl-N-phenyl-amino) triphenylamine and 9,10-bis(2'-naphthyl) anthracene (ADN) is used to sensitize the triplet-triplet annihilation (TTA) process on the ADN molecules. This results in a turn-on voltage (2.2 V) of the blue emission from the OLED below the bandgap (2.9 eV). From the transient electroluminescence measurement, blue emission totally came from the TTA process without direct recombination on the ADN molecules. The blue singlet exciton from the TTA process can be quenched by energy transfer to the exciplex, as revealed by transient photoluminescence measurements. This can be prevented by blocking the energy transfer path and improving the radiative recombination rate of blue emission. With the insertion of the "triplet diffusion and singlet blocking (TDSB)" layer and the incorporation of the dopant material, an ESTTA-OLED with external quantum efficiency of 5.1% was achieved, which consists of yellow and blue emission coming from the exciplex and ESTTA process, respectively.

Interrogating surface state of isolated and agglomerated PbS quantum dots with solvent-induced stress.

Applications of quantum dots (QDs) are often obstructed by the associated surface electronic states that quench photoluminescence (PL) and hinder charge transport. Preventing this is still largely being stymied owing to the lack of means to regulate their presence. Dispersing PbS QDs in toluene, we show that varying the solvent temperature offers a way of modulating their surface electronic state. A comprehensive energy-transfer model explains all the anomalous temperature-dependent behavior of the absorption and PL, explicitly revealing the PL quenching dynamics of isolated QDs due to the induced surface state by imposing solvent stress on their surface ligands. This study demonstrates that the local stress induced by a solvent can serve as a 'switch' for the surface electronic states of QDs, which is enabled by the well-studied thermo-physical properties of a liquid solvent.

Dependence of Adenine Raman Spectrum on Excitation Laser Wavelength: Comparison between Experiment and Theoretical Simulations.

We acquired the Raman spectra of adenine in powder and aqueous phase using excitation lasers with 532, 633, and 785 nm wavelengths for the region between 300 and 1500 cm-1. In comparison to the most distinct peak at 722 cm-1, the peaks between 1200 and 1500 cm-1 exhibited a characteristic increase in cross-section with decreasing excitation wavelength in both phases. This trend can be reproduced by different density functional theory (DFT) calculations for the adenine molecule in the gas phase as well as in the aqueous phase. Furthermore, from the calculation on the π-stacked dimer, hydrogen-bonded dimer, and trimer, we find that this trend toward excitation laser wavelength is not sensitive to the packing. When comparing the Raman spectra given by different excitation wavelength, one should take care in analyzing the cross-section, and present day DFT calculations are able to capture general trends in the excitation laser wavelength dependence of the Raman activity.

Rapid bacterial antibiotic susceptibility test based on simple surface-enhanced Raman spectroscopic biomarkers.

Rapid bacterial antibiotic susceptibility test (AST) and minimum inhibitory concentration (MIC) measurement are important to help reduce the widespread misuse of antibiotics and alleviate the growing drug-resistance problem. We discovered that, when a susceptible strain of Staphylococcus aureus or Escherichia coli is exposed to an antibiotic, the intensity of specific biomarkers in its surface-enhanced Raman scattering (SERS) spectra drops evidently in two hours. The discovery has been exploited for rapid AST and MIC determination of methicillin-susceptible S. aureus and wild-type E. coli as well as clinical isolates. The results obtained by this SERS-AST method were consistent with that by the standard incubation-based method, indicating its high potential to supplement or replace existing time-consuming methods and help mitigate the challenge of drug resistance in clinical microbiology.

Fabrication of Gold Nanoparticles/Graphene-PDDA Nanohybrids for Bio-detection by SERS Nanotechnology.

In this research, graphene nanosheets were functionalized with cationic poly (diallyldimethylammonium chloride) (PDDA) and citrate-capped gold nanoparticles (AuNPs) for surface-enhanced Raman scattering (SERS) bio-detection application. AuNPs were synthesized by the traditional citrate thermal reduction method and then adsorbed onto graphene-PDDA nanohybrid sheets with electrostatic interaction. The nanohybrids were subject to characterization including X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, and X-ray photoelectron spectroscopy (XPS). The results showed that the diameter of AuNPs is about 15-20 nm immobilized on the graphene-PDDA sheets, and the zeta potential of various AuNPs/graphene-PDDA ratio is 7.7-38.4 mV. Furthermore, the resulting nanohybrids of AuNPs/graphene-PDDA were used for SERS detection of small molecules (adenine) and microorganisms (Staphylococcus aureus), by varying the ratios between AuNPs and graphene-PDDA. AuNPs/graphene-PDDA in the ratio of AuNPs/graphene-PDDA = 4:1 exhibited the strongest SERS signal in SERS detection of adenine and S. aureus. Thus, it is promising in the application of rapid and label-free bio-detection of bacteria or tumor cells.