Sonu Gandhi

Strip-based immunochromatographic assay using specific egg yolk antibodies for rapid detection of morphine in urine samples.

Using specific egg yolk antibodies (IgY), a strip-based immunochromatographic assay was developed for rapid detection of morphine in urine samples. IgY type antibody against morphine was generated by immunizing chickens with well-characterized monoacetyl morphine-protein conjugate. The antibody was labeled with gold nanoparticles and used as an immunoprobe in the dipstick format for the visual detection of morphine in urine samples. The dipstick was developed using three membranes: an application pad made of glass fiber membrane to hold the tracer, a signal generation test line on nitrocellulose membrane (detection zone) and a cellulose membrane used as an absorption pad. Analytes of interest (morphine and its analogues) added to the sample well, dissolved the labeled antibody (tracer), and the antigen-antibody complex formed was transported by the flow caused by capillary action to the test line. The color signal of test line in proportion to the morphine concentration in urine samples was measured using a detector. The developed dipstick assay format was optimized, showing the average IC(50) values of morphine as low as 9.45 ng/mL, the detection range of 1-1000 ng/mL and the lowest detection limit 2.5 ng/mL under optimal conditions of analysis. The correlation between the developed dipstick and ELISA was 0.948 in the analysis of urine samples spiked with morphine. The developed dipstick could be a highly sensitive and convenient tool for rapid detection of opiate drugs in samples with high degree of stability.

Fluoroimmunoassay based on suppression of fluorescence self-quenching for ultra-sensitive detection of herbicide diuron

A highly sensitive heterogeneous fluoroimmunoassay has been developed for monitoring phenylurea herbicide diuron on the basis of suppression of fluorescence self-quenching. Specific antibody against diuron was produced and labeled with rhodamine isothiocyanate at different molar ratios and used as tracer in the developed immunoassay. The analytical sensitivity of immunoassay was enhanced by changing the microenvironment of fluorescence label with glycerin solution after the completion of immunoassay. Enhancer treatment on developed immunoassay showed improvement of fluorescence signal intensity by approximately 4-folds with higher stability compared with the signal determined without enhancer treatment of the wells. The immunoassay has a detection limit of 0.1 ng mL(-1) with good signal precision (approximately 2%) in the optimum working concentration range between 0.01 and 100 ng mL(-1) of diuron. In addition, the use of enhancer improved the stability of fluorescence signal by suppression of self-quenching of fluorescence signal. The proposed method has been applied satisfactorily for the ultra-sensitive detection of herbicide diuron in samples.

Direct Detection of Heroin Metabolites Using a Competitive Immunoassay Based on a Carbon‐Nanotube Liquid‐Gated Field‐Effect Transistor

Carbonnanotubes (CNTs) have attracted great attention in the field of sensing due to their exceptional charge-transport characteristics, which are confined to the nanotube surface and are able to detect molecular-level changes in their immediate environment.Ever since thefirstdemonstrationofCNTsensing capability on gas molecules, numerous studies have reported on the interaction of CNTs with a variety of biological and bioactive species such as proteins, peptides, DNA, enzymes, and the ability to transducer this interaction into an effective sensor. For the transduction of the sensing signal, diverse CNT sensor architectures have been employed. While popular electrochemistry approaches include CNT incorporated electrodes combined with cyclic voltammetry, amperometry, or impedance spectrometry, these devices normally require integration with electrochemical tags in order to translate surface-binding phenomena into a readable signal. In contrast, field-effect-transistor (FET)-based sensors allow analyte– receptor interaction to be directly translated into a readable electrical signal by monitoring conductance change in

Protein/carbon nanotubes interaction: The effect of carboxylic groups on conformational and conductance changes

Detailed understanding of interaction between biomolecules and single-walled carbon nanotubes (SWCNTs) is important in the design and applications of biosensors that employ SWCNTs for transduction of the analytes response. Reciprocal interactions of SWCNT with bovine serum albumin are investigated here with pristine and carboxylated nanotubes. Carboxylic functionalization was found to inflict a deeper change on protein conformation, than their pristine counterparts, accompanied with a change in nanotube conductance. This observation has significant implications for biosensors in highlighting the need to take into account the surface functionalization state of the active materials.

Recent advances in immunosensor for narcotic drug detection

Introduction: Immunosensor for illicit drugs have gained immense interest and have found several applications for drug abuse monitoring. This technology has offered a low cost detection of narcotics; thereby, providing a confirmatory platform to compliment the existing analytical methods. Methods: In this minireview, we define the basic concept of transducer for immunosensor development that utilizes antibodies and low molecular mass hapten (opiate) molecules. Results: This article emphasizes on recent advances in immunoanalytical techniques for monitoring of opiate drugs. Our results demonstrate that high quality antibodies can be used for immunosensor development against target analyte with greater sensitivity, specificity and precision than other available analytical methods. Conclusion: In this review we highlight the fundamentals of different transducer technologies and its applications for immunosensor development currently being developed in our laboratory using rapid screening via immunochromatographic kit, label free optical detection via enzyme, fluorescence, gold nanoparticles and carbon nanotubes based immunosensing for sensitive and specific monitoring of opiates.

An immunochromatographic dipstick as an alternate for monitoring of heroin metabolites in urine samples

Heroin use and addiction pose serious risks and side effects due to overdose. Quantification of heroin in biological samples is challenging due to rapid deacetylation of heroin to its active metabolites. In this study, we report the quantification of metabolic degradation of heroin by-products in biological urine samples. The presence of the drug was monitored after oral administration of heroin at different time intervals. Various biophysical techniques, such as high performance liquid chromatography (HPLC) and mass spectrometry (MS) were used to evaluate the presence of the drug. A competitive fluorescence based immunoassay was developed with a limit of detection (LOD) up to 0.01 ng mL−1 and the IC50 value was 0.1 ng mL−1, while the dipstick assay shows a LOD up to 5 ng mL−1. Rapid detection of narcotic drugs was carried out for biological urine samples collected at various time points. Validation of the developed dipstick was carried out for the standard as well as the spiked urine samples by fluorescence based immunoassay (FIA), using anti-morphine antibodies. A strong correlation (R = 0.94) was obtained between the developed dipstick and FIA assay for biological urine samples collected at various time points. The developed immunochromatographic dipstick is highly sensitive, field applicable and cost effective, and can serve as a first choice for the monitoring of narcotic drugs in blood, urine and saliva in drug addicts and athletes.

Chemiluminescence based immunoassay for the detection of heroin and its metabolites.

Introduction: Continuous use of opiates causes drug-related illnesses, which poses an alarming situation to develop sensitive detection platform. In this study, a highly sensitive and reliable chemiluminescence immunoassay (CI) has been developed for the detection of heroin and its major metabolites in spiked urine samples. Methods: To develop robust immunoassay, monoacetyl morphine-bovine serum albumin (MAM-BSA) conjugate was synthesized and characterized thoroughly by physicochemical techniques. The anti-MAM antibodies were developed, labeled with horseradish peroxidase (HRP) and immunoassay was developed to detect the presence of target drug in spiked urine samples. Results: A competitive CI was developed, where heroin, MAM, morphine, and codeine concentration were ranged from 0-1000 ng/ mL in spiked urine samples and limit of detection were 80, 95, 90, 75 pg/ mL. Conclusion: The developed CI is highly sensitive, specific, point of care, cost-effective and can be used as a routine technique for quantitative analysis for screening of narcotic drugs.

Liquid Gated Carbon Nanotubes Field Effect Transistors (LG-CNTFET) Platform for Herbicide Sensing

Single-walled carbon nanotube (SWCNT) is a one-dimensional system with all its carbon atoms present on the surface, hence its conductance is highly sensitive to the surrounding charge environment. Due to the extreme charge sensitivity, biocompatibility and chemical stability, SWCNT is particularly interested in biosensing application. In this paper, we demonstrated a practical approach of fabricating laminated SWCNT liquid gate field effect transistor (LGFET) through a solution processed route involving only two materials, PDMS and SWCNT. The laminated SWCNT LGFETs show great potential towards atrazine detection. The change in the detection signal in terms of conductance was deduced to be due to electrostatic gating mechanism caused by the localized interaction between CNT and the biomolecules. Although relatively high concentration was used in the experiment, the detection limit could be lowered down further by improving the signal-to-noise ratio of the measurement, which can be done through either signal amplification, and/or noise reduction.Copyright