Nanoporous alumina membranes have become a ubiquitous biosensing platform for a variety of applications and aptamers are being increasingly utilized as recognition elements in protein sensing devices. Combining the advantages of the two, we report label-free sensitive detection of human α-thrombin by an aptamer-functionalized nanoporous alumina membrane using a fourelectrode electrochemical cell. The sensor response to α-thrombin was determined in the presence of a high concentration (500 μM) of human serum albumin (HSA) as an interfering protein in the background. The sensor sensitivity was also characterized against γ-thrombin, which is a modified α-thrombin lacking the aptamer binding epitope. The detection limit, within an appreciable signal/ noise ratio, was 10 pM of α-thrombin in presence of 500 μM HSA. The proposed scheme involves the use of minimum reagents/sample preparation steps, has appreciable response in presence of high concentrations of interfering molecules and is readily amenable to miniaturization by association with existing-chip based electrical systems for application in point-of-care diagnostic devices.

Biosensors hold great potential for revolutionizing personalized medicine and environmental monitoring. Their construction is the key factor which depends on either manufacturing techniques or robust sensing materials to improve efficacy of the device. Functional graphene is an attractive choice for transducing material due to its various advantages in interfacing with biorecognition elements. Graphene and its derivatives such as graphene oxide (GO) are thus being used extensively for biosensors for monitoring of diseases. In addition, graphene can be patterned to a variety of structures and is incorporated into biosensor devices such as microfluidic devices and electrochemical and plasmonic sensors. Among biosensing materials, GO is gaining much attention due to its easy synthesis process and patternable features, high functionality, and high electron transfer properties with a large surface area leading to sensitive point-of-use applications. Considering demand and recent challenges, this perspective review is an attempt to describe state-of-the-art biosensors based on functional graphene. Special emphasis is given to elucidating the mechanism of sensing while discussing different applications. Further, we describe the future prospects of functional GO-based biosensors for health care and environmental monitoring with a focus on additive manufacturing such as 3D printing.

The binding/unbinding of the human thrombin and its 15-mer single stranded DNA aptamer, under the application of external stimulus in the form of electrostatic potential/electric field, is investigated by a combination of continuum analysis and atomistic molecular dynamics simulation. In agreement with the experiments that demonstrate the influence of electrostatic potential on the thrombin/aptamer complex, our computations show that the application of positive electric field successfully unbinds the thrombin from the aptamer. Results from umbrella sampling simulations reveal that there is a decrease in the free energy of binding between the thrombin and aptamer in presence of positive electric fields. Hydrogen bonding and non-bonded interaction energies, and hence the free energy of binding, between the thrombin and its aptamer reduce as the applied electric field is shifted from negative to positive values. Our analyses demonstrate that application of electrical stimulus modifies the molecular interactions within the complex and consequently, electrical field can be used to modulate the association between the thrombin and its aptamer.

No abstract

Experimental results show that the adsorption of the self assembled monolayers (SAMs) on a gold surface induces surface stress change that cause a deformation of the underlying substrate.However, the exact mechanism of stress development is yet to be elucidated. In the present study, multiscale computational models based on molecular dynamics (MD) simulations are applied to study the mechanism governing surface stress change. Distinct mechanisms for adsorption induced surface deformation, namely inter chain repulsion and thiol-gold interaction driven gold surface reconstruction, are investigated. Two different inter-atomic potentials, embedded atom method (EAM) and surface embedded atom method (SEAM), are used in the MD simulations to study the reconstruction induced surface stresses. Comparison of the predicted surface stress changes, resulting from MD and continuum mechanics based models, with observed experimental response, indicate that a modified SEAM based multiscale model can better capture the surface stress changes observed during alkanethiol SAM formation and gold surface reconstruction is the primary factor behind the surface stress change. Inter chain repulsions of SAM are found to have minimal contribution. Also, both the simulations and experiments show that surface stress change increases with surface coverage density and larger grain size.