Multiscale Sensing of Antibody–Antigen Interactions by Organic Transistors and Single-Molecule Force Spectroscopy

Abstract

Antibody-antigen (Ab-Ag) recognition is the primary event at the basis of many biosensing platforms. In label-free biosensors, these events occurring at solid-liquid interfaces are complex and often difficult to control technologically across the smallest length scales down to the molecular scale. Here a molecular-scale technique, such as single-molecule force spectroscopy, is performed across areas of a real electrode functionalized for the immunodetection of an inflammatory cytokine, viz. interleukin-4 (IL4). The statistical analysis of force-distance curves allows us to quantify the probability, the characteristic length scales, the adhesion energy, and the time scales of specific recognition. These results enable us to rationalize the response of an electrolyte-gated organic field-effect transistor (EGOFET) operated as an IL4 immunosensor. Two different strategies for the immobilization of IL4 antibodies on the Au gate electrode have been compared: antibodies are bound to (i) a smooth film of His-tagged protein G (PG)/Au; (ii) a 6-aminohexanethiol (HSC6NH2) self-assembled monolayer on Au through glutaraldehyde. The most sensitive EGOFET (concentration minimum detection level down to 5 nM of IL4) is obtained with the first functionalization strategy. This result is correlated to the highest probability (30%) of specific binding events detected by force spectroscopy on Ab/PG/Au electrodes, compared to 10% probability on electrodes with the second functionalization. Specifically, this demonstrates that Ab/PG/Au yields the largest areal density of oriented antibodies available for recognition. More in general, this work shows that specific recognition events in multiscale biosensors can be assessed, quantified, and optimized by means of a nanoscale technique.

Electrolytic Gated Organic Field-Effect Transistors for Application in Biosensors—A Review

“…Casalini et al [105] published more recently another work using Au gate as sensing area, instead of the semiconductor, using thiol-modified protein G or a 6-aminohexanethiol (HSC 6 NH 2 ) self-assembled monolayer followed by covalent coupling (protein G was used here for its property to bind IgG antibodies). They found that the most sensitive EGOFET was obtained with the first (affinity) immobilization strategy.…”

Label-free detection of interleukin-6 using electrolyte gated organic field effect transistors

“…6,7 The last years have witnessed a large number of studies attempting at developing label-free biosensors alternative to currently used platforms based on optical response. [8][9][10][11][12][13][14][15] As for IL-6, the latest reported biosensors that allow for a real-time monitoring of the cytokine levels without requiring secondary [33][34][35][36][37] .…”

High performing solution-coated electrolyte-gated organic field-effect transistors for aqueous media operation

“…Due to such interface sensitivity and water compatibility, EGOFETs can be turned into (bio)-transducers46. Accordingly, it has been possible to monitor different biological events such as host-guest recognition78, DNA hybridization9, or electro-catalysis of metabolites10, whose natural environment is the aqueous media. It was even demonstrated the potential to release drugs by playing with the electrical fields governing these types of devices11.…”

“…Among them, organic field-effect transistors provide a multi-parametric response showing features like (i) threshold voltage ( V th ), (ii) mobility ( μ ), (iii) on/off ratio ( I on / I off ), (iv) subthreshold slope ( SS ), and (v) transconductance ( g m ). Although the choice of using EGOFETs has many advantages for the development of multi-functional platforms interesting in the field of diagnostics12 and healthcare8, some unsolved problems are actually hindering their technological transfer such as their electrical stability. As a consequence, it is crucial to obtain a robust and efficient device that will be the core of a technology transferable to the electronic market.…”