title: 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.
authors: †Dipartimento di Scienze della Vita, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41125 Modena, Italy.
authors: Stefano
authors: S
authors: Casalini
authors: ‡Instituto de Ciencia de Materiales de Madrid (CSIC), 28049 Madrid, Spain.
authors: Andra C
authors: AC
authors: Dumitru
authors: Francesca
authors: F
authors: Leonardi
authors: †Dipartimento di Scienze della Vita, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41125 Modena, Italy.
authors: Carlo A
authors: CA
authors: Bortolotti
authors: ‡Instituto de Ciencia de Materiales de Madrid (CSIC), 28049 Madrid, Spain.
authors: Elena T
authors: ET
authors: Herruzo
authors: ⊥"Alma Mater Studiorum", Dipartimento di Chimica "G. Ciamician", Università di Bologna, Via Selmi 2, 40126 Bologna, Italy.
authors: Alessandra
authors: A
authors: Campana
authors: †Dipartimento di Scienze della Vita, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41125 Modena, Italy.|#Unesp, Postgraduate Program in Materials Science and Technology, São Paulo State University, 17033-360, Bauru, SP Brazil.
authors: Rafael F
authors: RF
authors: de Oliveira
authors: ∞"Alma Mater Studiorum", Dipartimento di Fisica e Astronomia, Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
authors: Tobias
authors: T
authors: Cramer
authors: ‡Instituto de Ciencia de Materiales de Madrid (CSIC), 28049 Madrid, Spain.
authors: Ricardo
authors: R
authors: Garcia
authors: †Dipartimento di Scienze della Vita, Università degli Studi di Modena e Reggio Emilia, Via Campi 183, 41125 Modena, Italy.
authors: Fabio
authors: F
authors: Biscarini
mesh_terms: D055910:Antibodies, Immobilized / Q000737:chemistry / Q000276:immunology; D000937:Antigen-Antibody Reactions; D001426:Bacterial Proteins / Q000737:chemistry; D004563:Electrochemistry; D006046:Gold / Q000737:chemistry; D018625:Microscopy, Atomic Force / Q000295:instrumentation*; D008958:Models, Molecular; D008968:Molecular Conformation; D036103:Nanotechnology / Q000295:instrumentation*; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014173:Transistors, Electronic
chemical_list: D055910:Antibodies, Immobilized; D001426:Bacterial Proteins; C034284:IgG Fc-binding protein, Streptococcus; D013438:Sulfhydryl Compounds; D006046:Gold
keywords: atomic force microscopy; bioelectronics; biorecognition; immunosensing; interleukin-4; organic field-effect transistors; single-molecule force spectroscopy