UV crosslinked poly(acrylic acid): a simple method to bio-functionalize electrolyte-gated OFET biosensors

Abstract

A simple and time-saving wet method to endow the surface of organic semiconductor films with carboxyl functional groups is presented. A thin layer of poly(acrylic acid) (pAA) is spin-coated directly on the electronic channel of an electrolyte-gated organic FET (EGOFET) device and cross-linked by UV exposure without the need for any photo-initiator. The carboxyl functionalities are used to anchor phospholipid bilayers through the reaction with the amino-groups of phosphatidyl-ethanolamine (PE). By loading the membranes with phospholipids carrying specific functionalities, such a platform can be easily implemented with recognition elements. Here the case of biotinylated phospholipids that allow selective streptavidin electronic detection is described. The surface morphology and chemical composition are monitored using SEM and XPS, respectively, during the whole process of bio-functionalization. The electronic and sensing performance level of the EGOFET biosensing platform is also evaluated. Selective analyte (streptavidin) detection in the low pM range is achieved, this being orders of magnitude lower than the performance level obtained by the well assessed surface plasmon resonance assay reaching the nM level, at most

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

“…Even though Buth et al used α-sexithiophene (α6T) in 2011 and 2012 to make an EGOFET-based biosensor [11,62], most EGOFET biosensors were reported with poly(3-hexylthiophene) (P3HT) as the organic semiconductors [8,32,60,[63][64][65][66][67][68][69][70][71][72]. In recent years, thienothiophene copolymers [73], especially the poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]-thiophene) (pBTTT) was also considered, due to a better stability in humid environment or even in water ( Figure 4) [74][75][76][77]. …”

“…Mulla et al [76] reported a pBTTT-based EGOFET sensor for streptavidin detection. pBTTT was spin-coated on the device, then a layer of poly(acrylic acid) was spin-coated on the pBTTT layer to have carboxyl functionalities acting as anchoring sites for phospholipid bilayers.…”

Recent Advances in Immobilization Strategies for Biomolecules in Sensors Using Organic Field-Effect Transistors

“…Mulla et al [48] proposed an innovative way to spincoat a thin layer of poly(acrylic acid) (PAA) on the top of PBTTT, and then UV-cross-linked PAA to obtain highdensity -COOH groups anchored on the surface of OSC film (Fig. 8).…”

“…Biotinylated phospholipids are anchored as bioprobes on the PAA coating through the EDC/NHS amine coupling chemistry. The electrical and sensing measurement are performed with an electrolyte-gated organic filed-effect transistor comprising a gold gate electrode and a droplet of PBS as a dielectric medium (reprinted from [48] with permission from RSC) These molecular probes acted like hapten and could bind to 2,4-D-specific Abs. The gold microelectrode performed scanning by applying a certain range of voltage in the diazo salt solution, which produced an insoluble thin layer on the metal electrode and completed the gate functionalization.…”

“…The introduction of a DNA molecule into an OFET sensor platform can not only enhance device performance, but also detect the target sequence based on the hybridization principle of DNA molecules. In a DNA molecular hybridization experiment, Lai Poly(acrylic acid) 0.01 nmol/L-1.6 mmol/L 10 pmol/L [48] et al [55] studied the hybridization mechanism under high ionic strength and deduced the principle of the adaptation of device structure design to sensing performance in another work, then optimized the layout of sensors and verified the possibility of pre-adjusting the device structure to enable a sensing function. Since the DNA molecule had a negatively charged phosphoric acid group, which introduced a positive bias between the gate and the source, the target DNA could be immobilized by electrostatic induction.…”