A new paper published this week by scientists from the Universities of Bath and Leeds, in the journal Biosensors and Bioelectronics (link is external), demonstrates the application of Affimer binders to biosensors for use within potential clinical diagnostics. Affimer reagents targeted to HER4 were immobilised upon an electrochemical sensor to form an Affimer-based biosensor for the detection of HER4. Characterisation of the Affimer-sensor revealed excellent target sensitivity in undiluted human serum across a very broad dynamic range, being able to accurately quantify HER4 concentration between 1pM and 100nM, with no observable matrix effect.
Within this study the researchers used electrochemical impedance sensors (EIS), which have recently gained attention as they offer label-free, fast and sensitive measurement with the possibility of miniaturised biosensor development. These sensors measure changes in impedance or capacitance that occur at an electrode surface through binding of the target protein to an immobilised capture protein, in this instance an anti-HER4 Affimer binder. Their benefits include concentration detection over a wide range, their low cost, rapid kinetics, and suitability for point-of-care diagnostics.
Antibodies have been used for the majority of biosensors generated to date, yet they show limitations through their lack of stability, large molecular size and complex and costly production. Affimer binders overcome these issues being highly stable, only 12-14kDa and both simple and inexpensive to produce. Consequently, the application of Affimer technology to biosensor applications opens the door to new platforms for alternative low cost and rapid multiplexed biosensors for a variety of targets.
HER4 is an emerging biomarker for gastrointestinal stromal tumours. This is the most common form of GI tumour and is showing an increasing prevalence in the population. The HER4 ectodomain has also been noted at low concentrations in the serum of breast cancer patients, where it could serve as part of a panel of biomarker offering prognostic or predictive information of a patient’s condition.
Affimer binders specific to the HER4 protein were immobilised to form a biorecognition layer upon gold electrodes and the sensor performance was monitored via a change in capacitance. Analysis of performance of the Affimer-sensor showed accurate concentration estimation over the range of 1pM to 100nM for the target protein, both within buffer and undiluted human serum, with a lower limit of detection below 1pM. The use of undiluted human serum within the assay did not affect the detection of HER4, with no observable off-target binding of the Affimer sensor to any proteins within the serum matrix or other additional proteins used to challenge the specificity of the biosensor.
Compared to the current commercially available antibody-based ELISA assays, this developed Affimer biosensor demonstrates improved sensitivity, with a much larger dynamic assay range (Commercial ELISA: 1-70pM; Affimer biosensor: 1pM-100nM), faster response times, ease of use and lower costs. These results exemplify the suitability of Affimer proteins for incorporation into biosensor platforms for a variety of targets, with the potential to create rapid, low cost, point-of-care diagnostics.