Real-Time, In Vivo Molecular Monitoring Using Electrochemical Aptamer Based Sensors: Opportunities and Challenges

Abstract

The continuous, real-time measurement of specific molecules in situ in the body would greatly improve our ability to understand, diagnose, and treat disease. The vast majority of continuous molecular sensing technologies, however, either (1) rely on the chemical or enzymatic reactivity of their targets, sharply limiting their scope, or (2) have never been shown (and likely will never be shown) to operate in the complex environments found in vivo . Against this background, here we review electrochemical aptamer-based (EAB) sensors, an electrochemical approach to real-time molecular monitoring that has now seen 15 years of academic development. The strengths of the EAB platform are significant: to date it is the only molecular measurement technology that (1) functions independently of the chemical reactivity of its targets, and is thus general, and (2) supports in vivo measurements. Specifically, using EAB sensors we, and others, have already reported the real-time, seconds-resolved measurements of multiple, unrelated drugs and metabolites in situ in the veins and tissues of live animals. Against these strengths, we detail the platform’s remaining weaknesses, which include still limited measurement duration (hours, rather than the more desirable days) and the difficulty in obtaining sufficiently high performance aptamers against new targets, before then detailing promising approaches overcoming these hurdles. Finally, we close by exploring the opportunities we believe this potentially revolutionary technology (as well as a few, possibly competing, technologies) will create for both researchers and clinicians.

Continuous optical detection of small-molecule analytes in complex biomatrices

“…9 However, stable and sensitive analyte detection in complex samples over extended periods of time generally remains a major challenge with electrochemical sensors, as outlined in previous work. 10 First, since detection is directly predicated on the ability of the redox reporter to interact with the electrode surface, electrode-based sensors are vulnerable to fouling from interferents present in the sample. Surface passivation strategies can mitigate this problem to some extent, 11 but fouling will inevitably occur when these sensors are deployed in complex mixtures over extended periods of time.…”

Selective Aptamer Modification of Au Surfaces in a Microelectrode Sensor Array for Simultaneous Detection of Multiple Analytes

“…Aptamers are used as the biorecognition elements that bind to a target analyte with high specificity and affinity and have gained widespread interest due to their high stability, low degree of immunogenicity, long shelf life, affordable production costs, and diverse binding capability (small molecules, proteins, nucleic acids), as compared to antibodies . A thiol linker is attached to the 5′ end of the aptamer to facilitate adsorption via self-assembled monolayer (SAM) formation on a gold electrode surface, while a redox-active molecule such as methylene blue (MB) is attached to the 3′ end, which enables a redox current to be measured. , …”

Single-cell Electrochemical Aptasensor Array

“…Compared to other methods, EC sensors have the merits of easy operation, high sensitivity, and portability. [10][11][12][13][14][15][16][17][18][19] For example, a recent technique using rolling circle amplification with aptamers could successfully demonstrate a limit of detection (LOD) as low as 5 CTC cells in whole blood (with 200 μL of the sample used for incubation). 20 Another approach using quantum dots as sensing probe attained a LOD of 2 cells/mL in human serum.…”