Part per Trillion Label-Free Electronic Bioanalytical Detection Maria Magliulo,* ,† Antonia Mallardi, ‡ Roberto Gristina, § Francesca Ridi, ∥,⊥ Luigia Sabbatini, † Nicola Cioffi, † Gerardo Palazzo, †,⊥ and Luisa Torsi † † Dipartimento di Chimica, Universita ̀ degli Studi di Bari “A. Moro” - Via Orabona, 4 70126 Bari, Italy ‡ CNR-IPCF, Istituto per i Processi Chimico-Fisici - Via Orabona, 4 70126 Bari, Italy § CNR-IMIP, Istituto di Metodologie Inorganiche e dei Plasmi - Via Orabona, 4 70126 Bari, Italy ∥ Dipartimento di Chimica − Universita ̀ degli Studi di Firenze − via della Lastruccia, 3 50019 Sesto Fiorentino, Italy ⊥ CSGI − Universita ̀ degli Studi di Firenze − via della Lastruccia, 3 50019 Sesto Fiorentino, Italy * S Supporting Information ABSTRACT: A Functional Bio-Interlayer Organic Field-Effect Transistor (FBI-OFET) sensor, embedding a streptavidin protein capturing layer, capable of performing label-free selective electronic detection of biotin at 3 part per trillion (mass fraction) or 15 pM, is proposed here. The response shows a logarithmic dependence spanning over 5 orders of magnitude of analyte concentration. The optimization of the FBI analytical performances is achieved by depositing the capturing layer through a controllable Layer-by-Layer (LbL) assembly, while an easy processable spin-coating deposition is proposed for potential low- cost production of equally highly performing sensors. Furthermore, a Langmuirian adsorption based model allows rationalizing the analyte binding process to the capturing layer. The FBI-OFET device is shown to operate also with an antibody interlayer as well as with an ad hoc designed microfluidic system. These occurrences, along with the proven extremely high sensitivity and selectivity, open to FBI-OFETs consideration as disposable electronic strip-tests for assays in biological fluids requiring very low detection limits. E lectronic bioanalytical detection performed by means of disposable plastic or paper devices has the potential to revolutionize the current approach to strip-testing. Presently, low-cost tests largely rely on lateral flow strips 1 that can deliver an analogic output, inherently not processable. An organic electronic sensing device would be capable, in principle, of producing a digital output allowing data processing for quantification purposes. Such devices can be produced by printing procedures likely at costs comparable to those of presently commercially available analogic strips. Eventually, the idea of a paper strip printed with an electronic biosensor circuit to be used as a disposable cartridge can be conceived as being capable of directly feeding a miniaturized reading system with a digital output. Such systems would be ideal to perform reliable analytical quantification at the point-of-need and at low-costs. Such a perspective is triggering a great amount of research activities in the field of organic electronic biodetection worldwide. 2−4 These endeavors involve the use of transistor sensing devices and see contributions proposing properly biofunctionalized silicon or carbon nanostructured electronic materials 5 as well as organic semiconductor (OS) thin-films. 6−8 The latter involved so far either the so-called electrolyte gated Organic Field-Effect Transistors (OFETs) 9,10 or bottom-gate, top-contact OFETs bearing a bilayer architecture as active layer. 11−13 The elicited bilayer is formed by a bioactive coating grafted on top of the OS, offering the advantage of the low-cost manufacturing procedures typically employed in organic electronics. 14 In a novel OFET sensor approach, the elicited bilayer is flipped so that the Functional Biological Interlayer (FBI) is placed underneath the OS, 15−17 in direct contact with the dielectric and right at the interface where the OFET two- dimensional transport occurs. 18,19 As already reported, 15 the direct interfacing between the biological capturing layer and the two-dimensional organic channel allows for electronically probing subtle changes occurring in the capturing layer while exposed to an external agent, eventually permitting the measurement of an extremely sensitive response. A detailed comparison between this technology and the state-of-the-art in OFET biosensors is extensively provided elsewhere. 15,20,21 Indeed, the FBI-OFETs show good electronic properties, while the biological activity of the interlayer is retained. The so far proposed FBI-OFETs included staking bilayer structures realized by spin-coating both the biological and the organic layers. 15,20 This paper proposes the study of FBI- OFETs embedding a streptavidin (SA) layer deposited either by electrostatic layer-by-layer (LbL) assembly 22 or by spin- coating, providing an assessment of the analytical performances for both structures. The LbL assembly approach allows for a more controlled deposition, and here it is used to optimize the analytical performance of the capturing layer. This deposition involves, on the other hand, procedural steps that are not easily Received: September 21, 2012 Accepted: January 16, 2013 Published: January 16, 2013 Article pubs.acs.org/ac © 2013 American Chemical Society 3849 dx.doi.org/10.1021/ac302702n | Anal. Chem. 2013, 85, 3849−3857