Colistin potentiation in multidrug-resistant Acinetobacter baumannii by a non-cytotoxic guanidine derivative of silver.

A novel nano-formulation (NF) that sensitizes Acinetobacter baumannii (AB) to otherwise ineffective colistin is described in the present study. Infections due to multidrug resistant (MDR) AB represent a major therapeutic challenge, especially in situations of pre-existing colistin resistance (colR). Subsequently, boosting the effectiveness of colistin would be a better alternative tactic to treat AB infections rather than discovering a new class of antibiotics. We have previously demonstrated an NF comprising self-assembled guanidinium and ionic silver nanoparticles [AD-L@Ag(0)] to have anti-biofilm and bactericidal activity. We report NF AD-L@Ag(0) for the very first time for the potentiation of colistin in Gram-negative colistin-resistant bacteria. Our results implied that a combination of clinically relevant concentrations of colistin and AD-L@Ag(0) significantly decreased colistin-resistant AB bacterial growth and viability, which otherwise was elevated in the presence of only colistin. In this study, we have described various combinations of minimum inhibitory concentration (MIC) of colistin (MICcol, 1/2 MICcol, and 1/4 MICcol) and that of AD-L@Ag(0) [MICAD-L@Ag(0), 1/2 MICAD-L@Ag(0), and 1/4 MICAD-L@Ag(0)] and tested them against MDR AB culture. The results (in broth as well as in solid media) signified that AD-L@Ag(0) was able to potentiate the anti-microbial activity of colistin at sub-MIC concentrations. Furthermore, the viability and metabolic activity of bacterial cells were also measured by CTC fluorescence assay and ATP bioluminescence assay. The results of these assays were in perfect concordance with the scores of cultures (colony forming unit and culture turbidity). In addition, quantitative real-time PCR (qRT-PCR) was performed to unveil the expression of selected genes, DNAgyrA, DNAgyrB, and dac. These genes introduce negative supercoiling in the DNA, and hence are important for basic cellular processes. These genes, due to mutation, modified the Lipid A of bacteria, further resisting the uptake of colistin. Therefore, the expression of these genes was upregulated when AB was treated with only colistin, substantiating that AB is resistant to colistin, whereas the combinations of MICcol + MICAD-L@Ag(0) downregulated the expression of these genes, implying that the developed formulation can potentiate the efficiency of colistin. In conclusion, AD-L@Ag(0) can potentiate the proficiency of colistin, further enhancing colistin-mediated death of AB by putatively disrupting the outer membrane (OM) and facilitating bacterial death.

Recent Advances and a Roadmap to Aptamer-Based Sensors for Bloodstream Infections.

The present review is intended to describe bloodstream infections (BSIs), the major pathogens responsible for BSIs, conventional tests and their limitations, commercially available methods used, and the aptamer and nanomaterials-based approaches developed so far for the detection of BSIs. The advantages associated with aptamers and the aptamer-based sensors, the comparison between the aptamers and the antibodies, and the various types of aptasensors developed so far for the detection of bloodstream infections have been described in detail in the present review. Also, the future outlook and roadmap toward aptamer-based sensors and the challenges associated with the aptamer development have also been concluded in this review.

Electrochemical Multiplexed Paper Nanosensor for Specific Dengue Serotype Detection Predicting Pervasiveness of DHF/DSS.

The serotype-specific early detection of dengue fever is very effective in predicting the pervasiveness of fatal infections such as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). This fever results from reinfection (secondary) with a serotype of the dengue virus, which is different from the serotype involved in primary infection. Hence, the present work was aimed to develop a multiplexed electrochemical paper-based analytical device (ePAD) consisting of graphene oxide-silicon dioxide (GO-SiO2) nanocomposites to detect the specific type of dengue virus (DENV). The conducting nature of GO-SiO2-coated multiplexed platform provided amplification in the signal response of the genosensor. The present sensor detected the target DNA of the four serotypes of the dengue virus, namely, DENV 1, DENV 2, DENV 3, and DENV 4, in a wide detection range of 100 pM to 100 µM. The sensor showed a high degree of specificity toward specific serotypes of DENV. Further, the use of such paper-based sensor had many advantages such as facile preparation, homogeneous distribution of nanoparticles onto the surface, requirement of a small quantity of sample, and low cost. To the best of our knowledge, this is the first report on the fabrication of a genosensor for predicting the pervasiveness of the dengue hemorrhagic fever or dengue shock syndrome.

Paper based point of care immunosensor for the impedimetric detection of cardiac troponin I biomarker.

Advancements in health care monitoring demand a rapid, accurate and reliable early diagnosis of "Heart Attack" (acute myocardial infarction) with an objective to develop a cost-effective, rapid and label-free point of care diagnostic test kit for the detection of cardiac troponin I (cTnI) on paper-based multi-frequency impedimetric transducers. Paper based sensing platforms were developed by integrating carboxyl group functionalized multi-walled carbon nanotubes (MWCNT) with antibodies of cardiac troponin I (anti-cTnI) biomarker and was characterized using Electrochemical Impedance Spectroscopy (EIS). Various concentrations of cTnI with anti cTnI were studied as a function of impedance change. The suitability of the proposed immunosensor is demonstrated by spiking cTnI in blood serum samples. The limit of detection (LoD) and sensitivity of the proposed sensor was determined to be 0.05 ng/mL and 1.85 mΩ/ng/mL respectively, with a response time of ~1 min. The shelf life of the fabricated sensor was nearly 30 days. The rapid response, very low detection limit, and cost effectiveness offer a portable platform to detect cTnI in blood serum samples. The proposed immunosensor, therefore, offers an affordable healthcare diagnostic platform in resource limited areas.

Comparative analysis of single-walled and multi-walled carbon nanotubes for electrochemical sensing of glucose on gold printed circuit boards.

In the present work, a comparative study was performed between single-walled carbon nanotubes and multi-walled carbon nanotubes coated gold printed circuit board electrodes for glucose detection. Various characterization techniques were demonstrated in order to compare the modified electrodes viz. cyclic voltammetry, electrochemical impedance spectroscopy and chrono-amperometry. Results revealed that single-walled carbon nanotubes outperformed multi-walled carbon nanotubes and proved to be a better sensing interface for glucose detection. The single-walled carbon nanotubes coated gold printed circuit board electrodes showed a wide linear sensing range (1 mM to 100 mM) with detection limit of 0.1 mM with response time of 5 s while multi-walled carbon nanotubes coated printed circuit board gold electrodes showed linear sensing range (1 mM to 100 mM) with detection limit of 0.1 mM with response time of 5 s. This work provided low cost sensors with enhanced sensitivity, fast response time and reliable results for glucose detection which increased the affordability of such tests in remote areas. In addition, the comparative results confirmed that single-walled carbon nanotubes modified electrodes can be exploited for better amplification signal as compared to multi-walled carbon nanotubes.

Detection of chikungunya virus DNA using two-dimensional MoS2 nanosheets based disposable biosensor.

Development of platforms for a reliable, rapid, sensitive and selective detection of chikungunya virus (CHIGV) is the need of the hour in developing countries. To the best of our knowledge, there are no reports available for the electrochemical detection of CHIGVDNA. Therefore, we aim at developing a biosensor based on molybdenum disulphide nanosheets (MoS2 NSs) for the point-of-care diagnosis of CHIGV. Briefly, MoS2 NSs were synthesized by chemical route and characterized using scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, Raman spectroscopy and X-Ray Diffraction. MoS2 NSs were then subjected to physical adsorption onto the screen printed gold electrodes (SPGEs) and then employed for the detection of CHIGV DNA using electrochemical voltammetric techniques. Herein, the role of MoS2 NSs is to provide biocompatibility to the biological recognition element on the surface of the screen printed electrodes. The detection strategy employed herein is the ability of methylene blue to interact differentially with the guanine bases of the single and double-stranded DNA which leads to change in the magnitude of the voltammetric signal. The proposed genosensor exhibited a wide linear range of 0.1 nM to 100 µM towards the chikungunya virus DNA.

Prussian blue nanocubes/carbon nanospheres heterostructure composite for biosensing of metformin.

This paper reports the fabrication of highly sensitive metformin sensor based on Prussian blue (PB) nanocubes/carbon nanosphere (CNS) heterostructures composed of a perfect cube and spherical composite on a fluorine-doped tin oxide surface. Due to the excellent biocompatibility of PB nanocubes the PB/CNS based Mf sensor exhibited a wide linear range of 0.001-10 mM with a response duration of less than 5 s and a detection limit (based on signal to noise ratio) of 0.1 µM.

Portable bioactive paper based genosensor incorporated with Zn-Ag nanoblooms for herpes detection at the point-of-care.

The present work describes the fabrication of an electrochemical paper-based analytical device (EPAD) integrated with Zn-Ag nanoblooms for detection of herpes in human, caused by Herpes virus 5(HHV-5) DNA, at the point of care. The cyclic voltammetry(CV) was used for electrochemical detection of the HHV-5 DNA in infected patient samples. The EPAD exihibited optimum current response within 5s at pH7.0 and 35°C with two dynamic linear/working ranges, 113-103 and 3×105-106copies/mL and detection limit of 97copies/mL. The device showed high selectivity, repeatability, and sensitivity. The device had many advantageous features such as portable, facile approach, economical and potential for commercialization. The proposed sensing scheme is highly feasible for future clinical detection of Herpes virus.

Hydrothermally synthesized zinc oxide nanorods incorporated on lab-on-paper device for electrochemical detection of recreational drug.

This paper reports an electrochemical paper analytical device (EPAD) for detection of recreational drug; methylenedioxymethamphetamine (MDMA). MDMA is used as an addictive narcotic by youth and there is an urgent need to detect this drug as it is a potential neurotoxic agent. The proposed EPAD represents many advantageous features of being simple, low-cost, consistent and disposable. The working electrode of the EPAD features zinc oxide nanorods (ZnONRs). The morphological, optical, elemental composition and phase analysis of the synthesized ZnONRs has been characterized by field emission scanning electron microscopy (FESEM), UV-Vis spectroscopy, energy dispersive X-ray spectroscopy (EDAX), photo-luminescence (PL) and X-ray diffraction (XRD). The developed sensor showed optimum response at 7.0 pH and wide linear range of 1 µM-1 mM with a low detection limit of 0.1 µM for MDMA. Evaluation of the sensor also revealed best results in terms of analytical recovery (95%) and accuracy (95%). The designed EPAD could prove to be very effective in case of forensic diagnostic applications. This work provides a reliable diagnostic method for remote areas with limited resources, and will also help people who cannot afford expensive medical tests and have limited access to power and trained personnel.

Detection of alprazolam with a lab on paper economical device integrated with urchin like Ag@ Pd shell nano-hybrids.

We present results of the studies relating to fabrication of a microfluidic biosensor chip based on urchin like Ag@ Pd shell nano-hybrids that is capable of sensing alprazolam through electrochemical detection. Using this chip we demonstrate, with high reliability and in a time efficient manner, the detection of alprazolam present in buffer solutions at clinically relevant concentrations. Methylene blue (MB) was also doped as redox transition substance for sensing alprazolam. Nano-hybrids modified EµPAD showed wide linear range 1-300ng/ml and low detection limit of 0.025ng/l. Low detection limit can further enhance its suitability for forensic application. Nano-hybrids modified EµPAD was also employed for determination of drug in real samples such as human urine. Reported facile lab paper approach integrated with urchin like Ag@ Pd shell nano-hybrids could be well applied for the determination of serum metabolites.

Lab on paper chip integrated with Si@GNRs for electroanalysis of diazepam.

We describe herein the fabrication of an electrochemical microfluidic paper based device (EµPAD) for the detection of diazepam, a sedative, anxiety-relieving and muscle-relaxing drug. To achieve it, silica coated gold nanorods (Si@GNRs) were synthesized and drop casted on an electrochemical microfluidic paper based device (EµPAD) for the detection of diazepam. The synthesized composites were characterized by recording its images in scanning electron microscope (SEM) and transmission electron microscope (TEM). The experimental results confirmed that Si@GNRs had good electrocatalytic activity towards diazepam. The modified paper based electrode showed a stable electrochemical response for diazepam in the concentration range of 3.5 nM to 3.5 mM. EµPAD offers many advantageous features such as facile approach, economical and have potential for commercialization. Si@GNRs modified EµPAD was also employed for determination of diazepam in spiked human urine samples. Reported facile lab paper approach integrated with Si@GNRs could be well applied for the determination of serum metabolites.

A genosensor for detection of consensus DNA sequence of Dengue virus using ZnO/Pt-Pd nanocomposites.

An electrochemical genosensor based on Zinc oxide/platinum-palladium (ZnO/Pt-Pd) modified fluorine doped tin oxide (FTO) glass plate was fabricated for detection of consensus DNA sequence of Dengue virus (DENV) using methylene blue (MB) as an intercalating agent. To achieve it, probe DNA (PDNA) was immobilized on the surface of ZnO/Pt-Pd nanocomposites modified FTO electrode. The synthesized nano-composites were characterized by high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-Vis spectroscopy, X-ray diffraction (XRD) analysis and Fourier transform infra-red (FTIR) spectroscopy. This PDNA modified electrode (PDNA/ZnO/Pt-Pd/FTO) served as a signal amplification platform for the detection of the target hybridized DNA (TDNA). The hybridization between PDNA and TDNA was detected by reduction in current, generated by interaction of anionic mediator, i.e., methylene blue (MB) with free guanine (3'G) of ssDNA. The sensor showed a dynamic linear range of 1 × 10-6M to 100 × 10-6M with LOD as 4.3 × 10-5 M and LOQ as 9.5 × 10-5 M. Till date, majorly serotype specific biosensors for dengue detection have been developed. The genosensor reported here eliminates the possibility of false result as in case of serotype specific DNA sensor. This is the report where conserved sequences present in all the serotypes of Dengue virus has been employed for fabrication of a genosensor.

Impedimetric genosensor for detection of hepatitis C virus (HCV1) DNA using viral probe on methylene blue doped silica nanoparticles.

An impedimetric genosensor was fabricated for detection of hepatitis C virus (HCV) genotype 1 in serum, based on hybridization of the probe with complementary target cDNA from sample. To achieve it, probe DNA complementary to HCVgene was immobilized on the surface of methylene blue (MB) doped silica nanoparticles MB@SiNPs) modified fluorine doped tin oxide (FTO) electrode. The synthesized MB@SiNPs was characterized using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) pattern. This modified electrode (ssDNA/MB@SiNPs/FTO) served both as a signal amplification platform (due to silica nanoparticles (SiNPs) as well as an electrochemical indicator (due to methylene blue (MB)) for the detection of the HCV DNA in patient serum sample. The genosensor was optimized and evaluated. The sensor showed a dynamic linear range 100-106 copies/mL, with a detection limit of 90 copies/mL. The sensor was applied for detection of HCV in sera of hepatitis patient and could be renewed. The half life of the sensor was 4 weeks. The MB@SiNPs/FTO electrode could be used for preparation of other gensensors also.

Graphene nanoflakes on transparent glass electrode sensor for electrochemical sensing of anti-diabetic drug.

Metformin (Mf) plays a major role in controlling insulin level of individuals at risk of developing diabetes mellitus. Overdose of Mf can cause lactic acidosis, diarrhoea, cough, or hoarseness, etc. These particulars point out the identification for selective and sensitive methods of Mf determination. In the present work, graphene nanoflakes-polymethylene blue (GNF-PMB) nano-composites were developed onto fluorine-doped tin oxide (SnO2/F) coated glass substrates for electrochemical sensing of Mf using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The developed sensor shows quick response time (10 s), linearity as 10-103 µM, LOD (0.1 nM), and good shelf life (10 weeks). Attempts have been made to utilize this electrode for estimation of Mf in urine samples. Configured as a highly responsive, reproducible Mf sensor, it combines the electrical properties of GNF and stable electron transfer of PMB. The newly developed Mf sensor presents a promising candidate in point-of-care diagnosis.

Point of care with micro fluidic paper based device integrated with nano zeolite-graphene oxide nanoflakes for electrochemical sensing of ketamine.

The present study was aimed to develop an ultrasensitive technique for electroanalysis of ketamine; a date rape drug. It involved the fabrication of nano-hybrid based electrochemical micro fluidic paper-based analytical device (EµPADs) for electrochemical sensing of ketamine. A paper chip was developed using zeolites nanoflakes and graphene-oxide nanocrystals (Zeo-GO). EµPAD offers many advantages such as facile approach, economical and potential for commercialization. Nanocrystal modified EµPAD showed wide linear range 0.001-5nM/mL and a very low detection limit of 0.001nM/mL. The developed sensor was tested in real time samples like alcoholic and non-alcoholic drinks and found good correlation (99%). The hyphenation of EµPAD integrated with nanocrystalline Zeo-GO for detection of ketamine has immense prospective for field-testing platforms. An extensive development could be made for industrial translation of this fabricated device.

An enzyme free Vitamin C augmented sensing with different ZnO morphologies on SnO2/F transparent glass electrode: A comparative study.

Three types of Zinc oxide (ZnO) nanostructures viz. ZnO nanocrystals (ZnONCs), ZnO nanoparticles (ZnONPs) and ZnO nanobelts (ZnONBs) were synthesized and characterized by UV-Vis, FTIR and SEM. A comparison of signal amplification by these ZnO nanostructures as judged by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Linear Sweep Voltammetry (LSV) revealed that ZnONCs are better sensing interface for electrochemical detection. When these ZnO nanostructure were compared electrochemically for sensing Vitamin C, ZnONC's sensor outperformed the ZnONP and ZnONB sensor and previously reported sensors. The ZnONCs/MB/FTO electrode showed a wide linear sensing range (0.001µM to 4000µM), low detection limit (0.0001µM), a small response time (5s) and a storage stability of 6months. To the best of our knowledge, this elevated sensitivity and remarkable stability for electrochemical Vitamin C detection using ZnONC's have not been reported so far.

Impedimetric genosensor for ultratrace detection of hepatitis B virus DNA in patient samples assisted by zeolites and MWCNT nano-composites.

Nanocrystals of zeolites (Nanocrys Zeo) and Multi-walled carbon nanotubes (MWCNT) based diagnostic genosensor was employed for detection of polymerase chain (PCR) amplified HBVDNA in blood of hepatitis B patients. The ssDNA-nanocomposite modified electrode was characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The hybridization between ss DNA probe and target ss DNA was detected by reduction in current, generated by interaction of methylene blue (MB) with free guanine (3'G) of ssDNA. Nanocrys zeo were deposited on the Fluorine doped tin oxide glass electrode (FTO) by drop-casting method for better immobilization of ss DNA while MWCNTs are incorporated into the zeolite-assembly to enhance the electro-conductivity of the present genosensor. The ssDNA-nanocomposite modified FTO electrode exhibited optimum current within 5s, at pH 5.6, and incubation temperature of 45°C. The value of charge transfer resistance (Rct) was linear with the number of copies of target DNA between 150 and 10(6) copies/ml. The limit of detection (LOD) of the sensor was 50 copies/ml. Within and between batches coefficients of variation (CV) were 2.5% and 3.2% respectively. Results obtained with our genosensor were also correlated with those by RT-PCR and r(2) value found with good accuracy of 97%. The electrode was reused by dipping it into 0.1M NaOH for 3min and lost 50% of its initial activity in 4 weeks. Furthermore the technique employed for detection of HBV is EIS, which is convenient and required less analysis time.

Hierarchical electrodeposition of methylene blue on ZnO nanocrystals thin films layered on SnO2/F electrode for in vitro sensing of anti-thalassemic drug.

Zinc oxide nanocrystals-methylene blue nanocomposites were developed by electrodeposition of methylene blue onto the thin films of zinc oxide nanocrystals deposited onto SnO2/F coated glass substrates for in vitro sensing of anti-thalassemic drug i.e. deferiprone. Detailed morphological, electrochemical, structural and optical characterizations of ZnONC-MB/FTO electrode were done using XRD, SEM, EIS, FTIR, LSV, and CV and show quick response time (within 5 s), linearity as 1 × 10(-3) to 10(3) µM and shelf life of about 10 weeks under refrigerated conditions. Attempts have been made to utilize this electrode for estimation of deferiprone in urine samples. The developed sensor exhibited high reproducibility and good storage stability.