A surface plasmon resonance immunoassay for the rapid analysis of methamphetamine in forensic oral fluid

Digital colloid-enhanced Raman spectroscopy for the pharmacokinetic detection of bioorthogonal drugs

Bioorthogonal drug molecules are currently gaining prominence for their excellent efficacy, safety and metabolic stability. Pharmacokinetic study is critical for understanding their mechanisms and guiding pharmacotherapy, which is primarily performed with liquid chromatography-mass spectrometry as the gold standard. For broader and more efficient applications in clinics and fundamental research, further advancements are especially desired in cheap and portable instrumentation as well as rapid and tractable pretreatment procedures. Surface-enhanced Raman spectroscopy (SERS) is capable of label-free detection of various molecules based on the spectral signatures with high sensitivity even down to a single-molecule level. But limited by irreproducibility at low concentrations and spectral interference in complex biofluids, SERS hasn't been widely applied for pharmacokinetics, especially in live animals. In this work, we propose a new method to quantify bioorthogonal drug molecules with signatures at the spectral silent region (SR) by the digital colloid-enhanced Raman spectroscopy (dCERS) technique. This method was first validated using 4-mercaptobenzonitrile in a mixture of analogous molecules, exhibiting reliable and specific identification capability based on the unique SR signature and Poisson-determined quantification accuracy. We further developed a single-step serum pretreatment method and successfully profiled the pharmacokinetic behavior of an anticancer drug, erlotinib, from animal studies. In a word, this method, superior in sensitivity, controllable accuracy, minimal background interference and facile pretreatment and measurement, promises diverse applications in fundamental studies and clinical tests of bioorthogonal drug molecules.

Rapid nanomolar detection of methamphetamine in biofluids via a reagentless electrochemical aptamer-based biosensor

The availability of sensing platforms able to rapidly measure abused drugs directly in biological fluids in a single step would allow performing drugged driving screening on the site. The achievement of this goal is extremely important for preventing and controlling drug abuse and crime incidence. Motived by this, we constructed a simple, cost-effective and reagentless electrochemical aptamer-based (EAB) sensor with methamphetamine (MAMP) as the target molecule. This EAB sensor produced a nanomolar level of detection accuracy in unprocessed or minimally processed bio-samples. Specifically, circular dichroic spectrum was used to confirm that the truncated aptamer from the original sequence would undergo large binding-induced conformational changes. We then engineered the aptamer to work in the EAB platform and the resulting sensor enabled sensitive and specific detection of MAMP with the detection limit of 30 nM in undiluted serum, 50 nM in undiluted urine and 20 nM in 50% saliva. The sensor has good recovery rate, implying this method has good reliability and repeatability. The detection limit is far below the clinical detection threshold, it would be hopefully used for preliminary screening of drugged driving in real world.

Emerging trends in point-of-care sensors for illicit drugs analysis

Consumption of illicit narcotic drugs and fatal or criminal activities under their influence has become an utmost concern worldwide. These drugs influence an individual's feelings, perceptions, and emotions by altering the state of consciousness and thus can result in serious safety breaches at critical workplaces. Point-of-care drug-testing devices have become the need-of-the-hour for many sections such as the law enforcement agencies, the workplaces, etc. for safety and security. This review focuses on the recent progress on various electrochemical and optical nanosensors developed for the analysis of the most common illicit drugs (or their metabolites) such as tetrahydrocannabinol (THC), cocaine (COC), opioids (OPs), amphetamines & methamphetamine, and benzodiazepine (BZDs). The paper also highlights the sensitivity and selectivity of various sensing modalities along with evolving parameters such as real-time monitoring and measurement via a smart user interface. An overall outlook of recent technological advances in point of care (POC) devices and guided insights and directions for future research is presented.

Open Circuit Potential as a Tool for the Assessment of Binding Kinetics and Reagentless Protein Quantitation

A microfluidic open circuit potential label-free protein assay was developed for the reagentless quantification of C-reactive protein (CRP), a model protein target, and further utilized to assess target-receptor binding kinetics. Generated sensors have very high baseline stabilities (<1% change in 100 min) and high levels of selectivity in complex media. Real-time assays are fast (<20 min), of high sensitivity (1 ng/mL limit of detection for CRP in serum), and resolve kinetic and thermodynamic characteristics that correlate well with those resolved optically. The assay shows excellent correlation with an enzyme-linked immunosorbent assay analysis of patient samples. The methodology has value in potentially underpinning a low-cost, rapid, and sensitive single-step biomarker quantification.

Recent Advancements in Receptor Layer Engineering for Applications in SPR-Based Immunodiagnostics

The rapid progress in the development of surface plasmon resonance-based immunosensing platforms offers wide application possibilities in medical diagnostics as a label-free alternative to enzyme immunoassays. The early diagnosis of diseases or metabolic changes through the detection of biomarkers in body fluids requires methods characterized by a very good sensitivity and selectivity. In the case of the SPR technique, as well as other surface-sensitive detection strategies, the quality of the transducer-immunoreceptor interphase is crucial for maintaining the analytical reliability of an assay. In this work, an overview of general approaches to the design of functional SPR-immunoassays is presented. It covers both immunosensors, the design of which utilizes well-known and often commercially available substrates, as well as the latest solutions developed in-house. Various approaches employing chemical and passive binding, affinity-based antibody immobilization, and the introduction of nanomaterial-based surfaces are discussed. The essence of their influence on the improvement of the main analytical parameters of a given immunosensor is explained. Particular attention is paid to solutions compatible with the latest trends in the development of label-free immunosensors, such as platforms dedicated to real-time monitoring in a quasi-continuous mode, the use of in situ-generated receptor layers (elimination of the regeneration step), and biosensors using recombinant and labelled protein receptors.

Automatic Sensing Setup for Methamphetamine Based on the Reactional Wettability Variation Strategy

An automatic setup for reactional wettability variation (RWV) was developed by interlinking liquid selection and transportation, object movement, and image recognition. In this way, the performance of the RWV strategy is updated to a nearly unmanned control manner with the example of methamphetamine and its aptamer. On the automatic RWV detection setup, the sensing surface acts similarly as before. The aptamer-based sensing surface resulted from the breakdown of the hydrophobic basis. The hydrophobicity is constructed on the metastable aptamer layer, which is responsive to the corresponding target. Methamphetamine interacts with its corresponding aptamer and destroys the basis of the hydrophobicity. A decrease in contact angle indicates the existence of methamphetamine. The RWV phenomenon is also affected by concentration and temperature. The development of an automatic detection ability would bring new possibilities to the surface reaction on smarter detection.

A surface plasmon resonance immunoassay for the rapid analysis of methamphetamine in forensic oral fluid

Background

Current chromatographic methods applied for the forensic analysis of methamphetamine are costly, time‐consuming, and require complicated pretreatment procedures. Thus, the rapid detection of methamphetamine is a critical and unmet need. In this study, a surface plasmon resonance (SPR) system based on indirect inhibitive immunoassay was designed for the analysis of methamphetamine in forensic oral fluid samples.

Methods

For the inhibition immunoassay, the diluted oral fluid was mixed with methamphetamine antibody and then injected into the SPR sensor chip. The biosensor chip was constructed by covalently immobilizing of methamphetamine‐bovine serum albumin conjugate onto a carboxymethyl dextran surface at an optimized pH. The concentration of antibody was also optimized.

Results

The SPR biosensor showed good sensitivity with a limit of detection of 0.44 ng/mL and was comparable or lower than the pre‐existing methods. The method was finally tested using oral fluid samples from 20 suspected drug abusers in forensic cases, and it provided an acceptable recovery of 113.2%, indicating good anti‐interference capability of the SPR sensor.

Conclusion

The SPR biosensor was rapid, reproducible, and had a great potential approach for the forensic detection of methamphetamine.