Portable Raman Analyzer Research Articles

3D Flexible SERS Substrates Integrated with a Portable Raman Analyzer and Wireless Communication for Point-of-Care Application

With the development of flexible surface-enhanced Raman spectroscopy (SERS) substrates that can realize rapid in situ detection, the SERS technique accompanied by miniaturized Raman spectrometers holds great promise for point-of-care testing (POCT). For an in situ detection strategy, constructing high-performance flexible and transparent SERS substrates through a facile and cost-effective fabrication method is critically important. Herein, we present a simple method for fabricating a large-area flexible and transparent SERS substrate consisting of a silver-nanoparticle-grafted wrinkled polydimethylsiloxane (Ag NPs@W-PDMS) film, using a surface-wrinkling technique and magnetron sputtering technology. By characterizing rhodamine 6G as a probe molecule with a portable Raman spectrometer, the flexible SERS substrate shows a low detection limit (10-7 M), a high enhancement factor (6.11 × 106), and excellent spot-spot and batch-batch reproducibilities (9.0% and 4.2%, respectively). Moreover, the Ag NPs@W-PDMS substrate maintains high SERS activity under bending and twisting mechanical deformations of over 100 cycles, as well as storage in air for 30 days. To evaluate its practical feasibility, in situ detection of malachite green on apple and tomato peels is performed with a detection limit of 10-6 M. In addition, for point-of-care analysis, we develop a wireless transmission system to transmit the collected SERS spectral data to a computer in real time for signal processing and analysis. Therefore, the proposed Ag NPs@W-PDMS SERS substrate fabricated through a simple and mass-producible method, combined with the utilization of a portable Raman spectrometer and wireless communication, offers a promising opportunity to extend the SERS technique from the laboratory to POCT applications.

Methodology for binary detection analysis of inkjet-printed optical sensors for chemical detection

We have developed inkjet-printed surface-enhanced Raman spectroscopy (SERS) sensors that are specifically designed to work with field portable Raman analyzers for the detection of chemical and biological agents (Tay et al. in J Raman Spectrosc, 2020). These SERS sensors are inkjet-printed on filter paper or fabric substrates. They are flexible and lightweight and provide point-of-sampling capabilities that other rigid planar SERS substrates lack. Conventionally, performance of a SERS substrate is characterized by its enhancement factor which is defined as the ratio of the normalized SERS to normal Raman intensity. This is an inadequate measure for a chemical/biological sensor. The performance of a chemical/biological sensor is best characterized by its sensitivity, probability of true positive detection, false positive rate, and its response time. The sensor using receiver operating characteristic (ROC) captures the performance trade-off between all these factors. Here, we outline the application of ROC analysis to the SERS sensors. This can be applied for all SERS sensors but we will focus its use with the printed SERS sensor. Specifically, the use of printed SERS sensor for the detection of fentanyl, a common opioid found in illicit drug, analyzed with ROC concept is demonstrated.

Quantitative Measurements of Codeine and Fentanyl on a Surface-Enhanced Raman-Active Pad Test.

The USA is in the midst of an opioid crisis that included over 60,000 overdose fatalities in 2017, mostly unintentional. This is due to excessive use of prescription opioids and the use of very strong synthetic opioids, such as fentanyl, mixed with illicit street drugs. The ability to rapidly determine if people or packages entering the country have or contain drugs could reduce their availability, and thereby decrease the use of illicit drugs. In an effort to address this problem, we have been investigating the ability of surface-enhanced Raman spectroscopy to detect trace amounts of opioids on clothing and packages. Here, we report the measurement of codeine and fentanyl at 100 ng/mL for 5 min on a pad impregnated with gold colloids, as well as a preliminary measurement of 500 pg of fentanyl on a glass surface using one of these pads. The calculated limit of detection for this measurement was 40 pg. This data strongly suggests that these pads, used with portable Raman analyzers, would be invaluable to airport security, drug raids, crime scenes, and forensic analysis.

Note: A portable Raman analyzer for microfluidic chips based on a dichroic beam splitter for integration of imaging and signal collection light paths.

An integrated and portable Raman analyzer featuring an inverted probe fixed on a motor-driving adjustable optical module was designed for the combination of a microfluidic system. It possesses a micro-imaging function. The inverted configuration is advantageous to locate and focus microfluidic channels. Different from commercial micro-imaging Raman spectrometers using manual switchable light path, this analyzer adopts a dichroic beam splitter for both imaging and signal collection light paths, which avoids movable parts and improves the integration and stability of optics. Combined with surface-enhanced Raman scattering technique, this portable Raman micro-analyzer is promising as a powerful tool for microfluidic analytics.

Fast identification and differentiation of mineral components in prostate stones using a portable fiber-optic Raman spectroscopy

We report a potential application of a portable fiber-optic Raman spectroscopy for fast prostatic calculi diagnosis. A portable Raman analyzer with a fiber-optic probe was first used to identify and differentiate the mineral components of prostate stones. The study indicates that three types of stones, hydroxyapatite (HA) stone, calcium oxalate dehydrate (COD) stone and mixed stone including HA, calcium oxalate monohydrate (COM) and COD, were directly detected from 15 patients with prostatic calculi in a short time. The present study reveals that this portable fiber-optic Raman spectroscopic technique was an easy and fast real-time tool to differentiate the mineral components in prostatic calculi.

A portable fiber-optic Raman analyzer for fast real-time screening and identifying cocrystal formation of drug-coformer via grinding process

A portable Raman analyzer with a fiber-optic probe was first used to rapidly screen and identify the cocrystal formation between drug and coformer. Indomethacin (IMC) and anhydrous theophylline (TP) were selected as model drugs, but saccharin (SAC) and anhydrous citric acid (CA) were chosen as model coformers. The cocrystal formation that occurred in the solid-state IMC–SAC or TP–CA system via mechanical grinding process was investigated. Differential scanning calorimetry (DSC) was also used to investigate the possible cocrystal formation. The present study indicates that this new portable fiber-opticRaman spectroscopic technique was an easy and fast “real-time” method to screen and identify the progressive cocrystal formation in solid-state IMC–SAC or TP–CA system in the process of mechanical grinding by inserting the probe directly into the ground mixtures.

The Use of Portable Raman Spectroscopy to Identify Conservation Treatments Applied to Heritage Stone

ABSTRACT Nondestructive in situ analysis of materials is highly desirable in cultural heritage studies, because it precludes the need for intensive sampling. The present study focused on the usability of Raman spectrometers, which can provide such analysis, in the identification of conservation treatments applied to stone materials forming part of the architectural heritage. Two products commonly used to conserve stone monuments, an ethylmethacrylate copolymer and an ethyl orthosilicate, were analyzed with a Raman spectrometer, both as supplied and after application to limestone. The main conclusion was that portable Raman analyzers can detect the presence and—in some cases—identify the nature of products on stone substrates. The latter is not always possible due to product-stone substrate interaction. The study clearly showed that a product and substrate database is needed for portable Raman spectroscopy to be usable in the analysis of conservation products, both before and after application to stone substrates.

Spectroscopic study of chemical compositions of cardiac calculus using portable Raman analyzer with a fiber-optic probe

Spectroscopic study of chemical compositions of cardiac calculus using portable Raman analyzer with a fiber-optic probe

Surface‐enhanced Raman spectra of melamine and other chemicals using a 1550 nm (retina‐safe) laser

Many trace chemical analyses are being transitioned from the lab to the field, among which is surface‐enhanced Raman spectroscopy. Although initial portable Raman analyzers primarily employ 785 nm laser excitation, recent studies suggest longer wavelengths, with an appropriate surface‐enhanced Raman‐active substrate, may provide equal sensitivity. Furthermore, 1550 nm excitation may provide added safety for the user, in that permanent retina damage does not occur. Here, we show that a reasonable enhancement factor can be obtained for melamine using 1550 nm laser excitation that is nearly equivalent to those obtained using 785 and 1064 nm laser excitation. We also demonstrate that a number of other chemicals of interest can be measured by 1550 nm surface‐enhanced Raman scattering, albeit only modest sensitivity is achieved because of instrument limitations, not enhancement factors. Copyright © 2011 John Wiley & Sons, Ltd.

Rapid Detection and Identification of Overdose Drugs in Saliva by Surface-Enhanced Raman Scattering Using Fused Gold Colloids

The number of drug-related emergency room visits in the United States doubled from 2004 to 2009 to 4.6 million. Consequently there is a critical need to rapidly identify the offending drug(s), so that the appropriate medical care can be administered. In an effort to meet this need we have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect and identify numerous drugs in saliva at ng/mL concentrations within 10 minutes. Identification is provided by matching measured spectra to a SERS library comprised of over 150 different drugs, each of which possess a unique spectrum. Trace detection is provided by fused gold colloids trapped within a porous glass matrix that generate SERS. Speed is provided by a syringe-driven sample system that uses a solid-phase extraction capillary combined with a SERS-active capillary in series. Spectral collection is provided by a portable Raman analyzer. Here we describe successful measurement of representative illicit, prescribed, and over-the-counter drugs by SERS, and 50 ng/mL cocaine in saliva as part of a focused study.

Raman Spectroscopy Using 1550 nm (Retina-Safe) Laser Excitation

During the past decade, the use of portable Raman analyzers for field measurements has grown dramatically. However, most analyzers use 785 nm excitation lasers that can cause permanent eye damage. To overcome this safety concern, we have built a portable Fourier transform (FT) Raman analyzer using a 1550 nm retina-safe excitation laser and have compared its performance to our 1064 nm FT-Raman analyzer, which uses the same optical design. Raman theory predicts approximately five times lower peak intensities at 1550 nm. Although we found that intensities were as much as 20 times less intense, the analyzer is still capable of measuring spectra of sufficient quality to identify and differentiate chemicals.

Rapid extraction and detection of trace Chlorpyrifos-methyl in orange juice by surface-enhanced Raman spectroscopy

It is estimated that 20–50% of crops are saved from infestation through the use of pesticides. However, US inspectors find that more than 4% of fruits and vegetables imported exceed concentration levels considered safe for human consumption. This represents millions of tons of food brought to market annually that cannot be inspected using current hour-long laboratory methods. In an effort to provide inspectors with a simple, fast, field-usable analyzer and method, we have been developing a sampling device that includes surface-enhanced Raman spectroscopy (SERS) to detect, identify, and quantify pesticides below part-per-million (μg/mL) concentrations in approximately 10 min using a portable Raman analyzer. The entire method, including solvent extraction, solid-phase extraction, and SERS-detection, was used to detect 50 parts-per-billion (ppb) Chlorpyrifos-methyl (CPM) artificially added to orange juice in 12 min. The same method and analyzer can be readily adapted to other pesticides and foods.

A SERS-BASED ANALYZER FOR POINT AND CONTINUOUS WATER MONITORING OF CHEMICAL AGENTS AND THEIR HYDROLYSIS PRODUCTS

Protection of military personnel and civilians from water supplies poisoned by chemical warfare agents (CWAs) requires an analyzer that has sufficient sensitivity (μg/L, ppb), specificity (differentiate the CWA from its hydrolysis products), and speed (less than 10 minutes) to be of value. In an effort to meet these requirements, we have been investigating the ability of surface-enhanced Raman spectroscopy (SERS) to detect cyanide and sulfur mustard in water. In our work, we have developed a novel SERS-active material that consists of a porous glass with trapped metal particles. Previously, we coated the inside walls of glass vials and measured cyanide at 1 mg/L in water in as little as 1 minute. However, measurements of sulfur mustard have only been measured to 10 mg/L. Recently, we filled glass capillaries with the SERS-active material. Here we describe measurements of cyanide, sulfur mustard, and it's hydrolysis product, thiodiglycol, using these capillaries and a portable Raman analyzer suitable for point and continuous water monitoring.