Impact of the Coverage of Aptamers on a Nanoparticle on the Binding Equilibrium and Kinetics between Aptamer and Protein

Knowledge of the interaction between aptamer and protein is integral to the design and development of aptamer-based biosensors. Nanoparticles functionalized with aptamers are commonly used in these kinds of sensors. As such, studies into how the number of aptamers on the nanoparticle surface influence both kinetics and thermodynamics of the binding interaction are required. In this study, aptamers specific for interferon gamma (IFN-γ) were immobilized on the surface of gold nanoparticles (AuNPs), and the effect of surface coverage of aptamer on the binding interaction with its target was investigated using fluorescence spectroscopy. The number of aptamers were adjusted from an average of 9.6 to 258 per particle. The binding isotherm between AuNPs-aptamer conjugate and protein was modeled with the Hill-Langmuir equation, and the determined equilibrium dissociation constant (K′D) decreased 10-fold when increasing the coverage of aptamer. The kinetics of the reaction as a function of coverage of aptamer were also investigated, including the association rate constant (kon) and the dissociation rate constant (koff). The AuNPs-aptamer conjugate with 258 aptamers per particle had the highest kon, while the koff was similar for AuNPs-aptamer conjugates with different surface coverages. Therefore, the surface coverage of aptamers on AuNPs affects both the thermodynamics and the kinetics of the binding. The AuNPs-aptamer conjugate with the highest surface coverage is the most favorable in biosensors considering the limit of detection, sensitivity, and response time of the assay. These findings deepen our understanding of the interaction between aptamer and target protein on the particle surface, which is important to both improve the scientific design and increase the application of aptamer-nanoparticle based biosensor

Single particle detection of protein molecules using dark-field microscopy to avoid signals from nonspecific adsorption

A massively parallel single particle sensing method based on core-satellite formation of Au nanoparticles was introduced for the detection of interleukin 6 (IL-6). This method exploits the fact that the localized plasmon resonance (LSPR) of the plasmonic nanoparticles will change as a result of core-satellite formation, resulting in a change in the observed color. In this method, the hue (color) value of thousands of 67 nm Au nanoparticles immobilized on a glass coverslip surface is analyzed by a Matlab code before and after the addition of reporter nanoparticles containing IL-6 as target protein. The average hue shift as the result of core-satellite formation is used as the basis to detect small amount of proteins. This method enjoys two major advantages. First it is able to analyze the hue values of thousands of nanoparticles in parallel in less than a minute. Secondly the method is able to circumvent the effect of non-specific adsorption, a major issue in the field of biosensing

Locked nucleic acid molecular beacon for multiplex detection of loop mediated isothermal amplification

Loop mediated isothermal amplification (LAMP) holds incredible promise for point - of - care molecular diagnostics because of its high sensitivity and isothermal amplification behaviour. The issues related to the spurious non-specific amplification caused by the template independent amplification of primers itself causes false positive detection. This can be exacerbated by the common indirect methods used for detection of LAMP. Developing robust and specific detection methods for LAMP is a challenge due to the complex nature of the LAMP amplicons. To see wider adaptation of LAMP, we employ locked nucleic acid bases in molecular beacon to provide the structural stability to the hairpin probes that enable specific and multiplex detection of LAMP. Locked nucleic acid (LNA) modification provides ultra - high thermal stability to the molecular beacons resulting in negligible background fluorescence in the closed state. In this study, various combinations of LNA modifications in the stem and loop region were used and characterized for their thermal stability and influence on hybridization efficiency. The sequence specificity and ultra - high thermal stability of the LNA bases was exploited to develop a multiplex LAMP assay for detection of clinically important antibiotic resistance in S.aureus in 30 min. Multiplex approaches hold a significant advancement in LAMP and would find widespread applications in molecular diagnostics

DNA-hybridisation detection on Si(100) surfaces using lightactivated electrochemistry: a comparative study between bovine serum albumin and hexaethylene glycol as antifouling layers

Light can be used to spatially resolve electrochemical measurements on a semiconductor electrode. This phenomenon has been explored to detect DNA hybridization with light-addressable potentiometric sensors and, more recently, with light-addressable amperometric sensors based on organic-monolayer-protected Si(100). Here, a contribution to the field is presented by comparing sensing performances when bovine serum albumin (BSA) and hexaethylene glycol (OEG₆) are employed as antifouling layers that resist nonspecific adsorption to the DNA-modified interface on Si(100) devices. What is observed is that both sensors based on BSA or OEG₆ initially allow electrochemical distinction among complementary, noncomplementary, and mismatched DNA targets. However, only surfaces based on OEG₆ can sustain electroactivity over time. Our results suggest that this relates to accelerated SiO_<i>x</i> formation occasioned by BSA proteins adsorbing on monolayer-protected Si(100) surfaces. Therefore, DNA biosensors were analytically explored on low-doped Si(100) electrodes modified on the molecular level with OEG₆ as an antifouling layer. First, light-activated electrochemical responses were recorded over a range of complementary DNA target concentrations. A linear semilog relation was obtained from 1.0 × 10^–11 to 1.0 × 10^–6 mol L^–1 with a correlation coefficient of 0.942. Then, measurements with three independent surfaces indicated a relative standard deviation of 4.5%. Finally, selectivity tests were successfully performed in complex samples consisting of a cocktail mixture of four different DNA sequences. Together, these results indicate that reliable and stable light-activated amperometric DNA sensors can be achieved on Si(100) by employing OEG₆ as an antifouling layer

Systematic review of the impact of point-of-care testing for influenza on the outcomes of patients with acute respiratory tract infection

© 2018 John Wiley & Sons, Ltd. Acute respiratory tract infections are a major cause of morbidity and mortality and represent a significant burden on the health care system. Laboratory testing is required to definitively distinguish infecting influenza virus from other pathogens, resulting in prolonged emergency department (ED) visits and unnecessary antibiotic use. Recently available rapid point-of-care tests (POCT) may allow for appropriate use of antiviral and antibiotic treatments and decrease patient lengths of stay. We undertook a systematic review to assess the effect of POCT for influenza on three outcomes: (1) antiviral prescription, (2) antibiotic prescription, and (3) patient length of stay in the ED. The databases Medline and Embase were searched using MeSH terms and keywords for influenza, POCT, antivirals, antibiotics, and length of stay. Amongst 245 studies screened, 30 were included. The majority of papers reporting on antiviral prescription found that a positive POCT result significantly increased use of antivirals for influenza compared with negative POCT results and standard supportive care. A positive POCT result also led to decreased antibiotic use. The results of studies assessing the effect of POCT on ED length of stay were not definitive. The studies assessed in this systematic review support the use of POCT for diagnosis of influenza in patients suffering an acute respiratory infection. Diagnosis using POCT may lead to more appropriate prescription of treatments for infectious agents. Further studies are needed to assess the effect of POCT on the length of stay in ED

Two sittings of Autologous Bone Marrow Stem Cells within two years in a case of Ischemic Cardiomyopathy

A 66yrs old Diabetic and Hypertensive female, who had Anterior Wall MI 5yrs ago and had undergone PTCA with Stent to LAD, was admitted for refractory CHF with Severe LVD 2yrs ago and the LVEF then was 25%. Coronary Angiogram was done which showed Total Occlusion of LAD and 50% Stenosis of RCA. Method: 100ml of her bone marrow was harvested from posterior iliac crest and the BMMNCs were isolated as per cGMP protocols at NCRM, Chennai and 325X106 cells with a CD34+ count of 0.84% were injected the next day by transfemoral catheter into the coronary arteries. Post treatment she had clinical improvement. EF increased by 5%. She was in Class-II for 1 year. After 1 yr, she was admitted with severe CHF and EF had deteriorated to 20%. This time BMMNCs isolated from the bone marrow were subjected to in vitro expansion by which the initial 0.15% CD34+ cells increased by nearly 30 fold to 4.62%. Totally 315X106 cells were injected into the coronaries. Post treatment there is clinical as well as Echo evidence of improvement and BNP level has come down by 30%. Conclusion:　 Isolated and expanded CD34+ cells from bone marrow mononuclear cells of autologous origin, administered into the coronaries in an Ischemic Cardiomyopathy patient has been proven to be safe. The clinical and Echo cardiographic improvement that has sustained for long-term, proves the feasibility and efficacy of two consecutive autologous bone marrow stem cell applications, one isolated and the second ex vivo expanded. More case studies may be undertaken to further evaluate the results

Optical tweezers-based characterisation of gold core-satellite plasmonic nano-assemblies incorporating thermo-responsive polymers

We report on the characterisation of the optical properties and dynamic behaviour of optically trapped single stimuli-responsive plasmonic nanoscale assemblies. Nano-assemblies consist of a core-satellite arrangement where the constituent nanoparticles are connected by the thermoresponsive polymer, poly(DEGA-co-OEGA). The optical tweezers allow the particles to be held isolated in solution and interrogated using dark-field spectroscopy. Additionally, controlling the optical trapping power provides localised heating for probing the thermal response of the nanostructures. Our results identify a number of distinct core-satellite configurations that can be stably trapped, which are verified using finite element modelling. Laser heating of the nanostructures through the trapping laser yields irreversible modification of the arrangement, as observed through the scattering spectrum. We consider which factors may be responsible for the observed behaviour in the context of the core-satellite geometry, polymer-solvent interaction, and the bonding of the nanoparticles