A simple and label-free aptasensor based on amino group-functionalized gold nanocomposites-Prussian blue/carbon nanotubes as labels for signal amplification

Advances in Electrochemical Aptasensors Based on Carbon Nanomaterials

Carbon nanomaterials offer unique opportunities for the assembling of electrochemical aptasensors due to their high electroconductivity, redox activity, compatibility with biochemical receptors and broad possibilities of functionalization and combination with other auxiliary reagents. In this review, the progress in the development of electrochemical aptasensors based on carbon nanomaterials in 2016–2020 is considered with particular emphasis on the role of carbon materials in aptamer immobilization and signal generation. The synthesis and properties of carbon nanotubes, graphene materials, carbon nitride, carbon black particles and fullerene are described and their implementation in the electrochemical biosensors are summarized. Examples of electrochemical aptasensors are classified in accordance with the content of the surface layer and signal measurement mode. In conclusion, the drawbacks and future prospects of carbon nanomaterials’ application in electrochemical aptasensors are briefly discussed.

In Vivo Use of a Multi-DNA Aptamer-Based Payload/Targeting System To Study Dopamine Dysregulation in the Central Nervous System

The delivery of therapeutics across the blood-brain barrier remains a considerable challenge in investigating central nervous system related processes. In this work, a liposome vehicle was surface-modified with an aptamer that binds to the transferrin receptor and was loaded with two different dopamine-binding aptamer payloads. This system was effectively used to promote the delivery of the aptamer cargo from the peripheral injection site into the brain. The effect of these delivered aptamers on behavior was investigated in vivo in a locomotor task. The first dopamine binding aptamer assessed was a DNA aptamer, the binding of which had been previously validated through the aptamer-based biosensor development reported by several independent research groups. The second aptamer investigated was the result of a novel in vitro selection experiment described herein. Our data suggest that systemic administration of the modified liposomes led to delivery of the dopamine aptamers into the brain. Fluorescence microscopy revealed differential distribution of fluorescence based on the presence or absence of the transferrin receptor aptamer on the surface of fluorescently modified liposomes. In a behavioral experiment using cocaine administration to induce elevated concentrations of neural dopamine, systemic pretreatment with the dopamine aptamer-loaded liposomes reduced cocaine-induced hyperlocomotion. Multiple controls including a transferrin-negative liposome control and transferrin-positive liposomes loaded with either a nonbinding, base-substituted dopamine aptamer or a random oligonucleotide were investigated. None of these controls altered cocaine-induced hyperlocomotion. Chronic systemic administration of the modified liposomes produced no deleterious neurobehavioral or neural degenerative effects. Importantly, this work is one example of an application for this versatile multiaptamer payload/targeting system. Its general application is limited only by the availability of aptamers for specific neural targets.

Reduced graphene oxide/nile blue/gold nanoparticles complex-modified glassy carbon electrode used as a sensitive and label-free aptasensor for ratiometric electrochemical sensing of dopamine

In this work, glassy carbon electrode (GCE) surface was modified by drop-coating graphene oxide (GO) and nile blue (NB) to form GO/NB/GCE. By using a one-step coreduction treatment under cyclic voltammetry (CV) scanning, gold nanoparticles (AuNPs) were electrodeposited onto GO/NB/GCE surface, simultaneously generating reduced GO (rGO). AuNPs from the prepared rGO/NB/AuNPs/GCE was combined with 5'-SH-terminated aptamer of dopamine (DA) via Au-S coupling to fabricate aptamer-rGO/NB/AuNPs/GCE system. DA specifically combined with its aptamer modified on rGO/NB/AuNPs/GCE surface. CV, electrochemical impedance spectroscopy, square wave voltammetry responses of this system as the working electrode were measured. With the addition of DA, the peak current intensities located at -0.45 V (I_NB) and 0.15 V (I_DA) showed gradually decreased and increased changes, respectively. There was a good linear (R² = 0.9922) relationship between lg(I_DA/I_NB) and the logarithm of DA concentration (lgC_DA) in the C_DA range from 10 nM to 0.2 mM, showing a low detection limit of 1 nM. This system as a novel, sensitive and label-free aptasensor was used for ratiometric electrochemical sensing of DA. Experimental results verified that this aptasensor possessed high stability, selectivity and sensitivity towards DA detection, over potential interferents. This aptasensor efficiently determined DA in real biological samples, together with high detection recoveries of 97.0-104.0%.

Progress in utilisation of graphene for electrochemical biosensors

This review discusses recent graphene (GR) electrochemical biosensor for accurate detection of biomolecules, including glucose, hydrogen peroxide, dopamine, ascorbic acid, uric acid, nicotinamide adenine dinucleotide, DNA, metals and immunosensor through effective immobilization of enzymes, including glucose oxidase, horseradish peroxidase, and haemoglobin. GR-based biosensors exhibited remarkable performance with high sensitivities, wide linear detection ranges, low detection limits, and long-term stabilities. Future challenges for the field include miniaturising biosensors and simplifying mass production are discussed.