Here we report on the fabrication of reconfigurable and solution processable nanoscale biosensors with multisensing capability, based on single-walled carbon nanotubes (SWCNTs). Distinct DNA-wrapped (hence water-soluble) CNTs were immobilized from solution onto different prepatterned electrodes on the same chip, via a low-cost dielectrophoresis (DEP) methodology. The CNTs were functionalized with specific, and different, aptamer sequences that were employed as selective recognition elements for biomarkers indicative of stress and neuro-trauma conditions. Multiplexed detection of three different biomarkers was successfully performed, and real-time detection was achieved in serum down to physiologically relevant concentrations of 50 nM, 10 nM, and 500 pM for cortisol, dehydroepiandrosterone-sulfate (DHEAS), and neuropeptide Y (NPY), respectively. Additionally, the fabricated nanoscale devices were shown to be reconfigurable and reusable via a simple cleaning procedure. The general applicability of the strategy presented, and the facile device fabrication from aqueous solution, hold great potential for the development of the next generation of low power consumption portable diagnostic assays for the simultaneous monitoring of different health parameters.

parallel electroless plating, [16] and shadow mask evaporation, [17,18] and the field has recently been reviewed. [19,20] Meanwhile new parallel fabrication strategies for formation of nanogap electrodes are being developed, here recent examples include mole cular crystal lithography, [21] gold nanorod alignment, [22] crack-defined electronic nanogaps, [23] self-limiting electrode growth, [24] the use of graphenebased constrictions, [25] and carbon nanotube electrodes. [26,27] A remaining challenge is scalability, that is, how to position single (or a few) molecules in the nanogap in a parallel way. In this context, an interesting approach is the use of the protodevice concept, where the single (or a few) molecule is isolated in the solution between nanoparticles, and subsequently self-assembled onto prefabricated nanoelectrodes. [28][29][30][31][32][33][34] Templated self-assembly can be used to position nanoparticles at prefabricated surfaces. Examples include positioning of gold nanoparticles and orientation of gold nanorods. [35,36] It is also possible to assemble particles using a meniscus flow over nanostructures, [37,38] chemically activate and passivate parts of a surface prior to deposition of nanoparticles, [39] making use of variations of hydrophobicity on a surface [40] or wet-contact printing. [41] Other methods involve electrostatic trapping of particles attached with molecules. [42][43][44] Here we explore the natural surface charges that different metal/metal oxides acquire in solution to guide bottom-up assembled molecular linked nanoparticle dimers to prefabricated electrodes (Figure 1). It is in this manner possible to position, isolate, and measure electron transport on a single (or a few) molecules. Electron-beam lithography (EBL) was used to fabricate electrode pairs, with optimized geometry and materials to promote the assembly of negatively charged nanoparticle dimers (Figure 2). The electrodes are made in layers of nickel (Ni) and palladium (Pd). Nickel has proven to be able to attract negatively charged citrate stabilized nanoparticles due to the positive surface potential at pH 6.5-7. [45] Pd is sandwiched between the Ni electrodes to improve the conductivity of the electrodes, and to enable an oxide free interface between the electrodes and protodevices. At the same time the top Pd layer reduces assembly of nanoparticles "on top" of the electrodes. Two different molecules, 1,6-hexanedithiol and 1,4-benzenedithiol, were used as test molecules for the construction of Single molecule electronics might be a way to add additional function to nanoscale devices and continue miniaturization beyond current state of the art. Here, a combined top-down and bottom-up strategy is employed to assemble single molecules onto prefabricated electrodes. Protodevices, which are self-assembled nanogaps composed by two gold nanoparticles linked by a single or a few molecules, are guided onto top-down prefabricated nanosized nickel electrodes with sandwiched palladium layers. It is shown that an optimized geo...

The ability to detect proteins through gating conductance by their unique surface electrostatic signature holds great potential for improving biosensing sensitivity and precision. Two challenges are: (1) defining the electrostatic surface of the incoming ligand protein presented to the conductive surface; (2) bridging the Debye gap to generate a measurable response. Herein, we report the construction of nanoscale protein‐based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets. Using a β‐lactamase binding protein (BLIP2) as the capture protein attached to carbon nanotube field effect transistors in different defined orientations. Device conductance had influence on binding TEM‐1, an important β‐lactamase involved in antimicrobial resistance (AMR). Conductance increased or decreased depending on TEM‐1 presenting either negative or positive local charge patches, demonstrating that local electrostatic properties, as opposed to protein net charge, act as the key driving force for electrostatic gating. This, in turn can, improve our ability to tune the gating of electrical biosensors toward optimized detection, including for AMR as outlined herein.

The ability to detect proteins through gating conductance by their unique surface electrostatic signature holds great potential for improving biosensing sensitivity and precision. Two challenges are: (1) defining the electrostatic surface of the incoming ligand protein presented to the conductive surface; (2) bridging the Debye gap to generate a measurable response. Herein, we report the construction of nanoscale protein‐based sensing devices designed to present proteins in defined orientations; this allowed us to control the local electrostatic surface presented within the Debye length, and thus modulate the conductance gating effect upon binding incoming protein targets. Using a β‐lactamase binding protein (BLIP2) as the capture protein attached to carbon nanotube field effect transistors in different defined orientations. Device conductance had influence on binding TEM‐1, an important β‐lactamase involved in antimicrobial resistance (AMR). Conductance increased or decreased depending on TEM‐1 presenting either negative or positive local charge patches, demonstrating that local electrostatic properties, as opposed to protein net charge, act as the key driving force for electrostatic gating. This, in turn can, improve our ability to tune the gating of electrical biosensors toward optimized detection, including for AMR as outlined herein.

Controlled deposition of colloidal nanoparticles using self-assembly is a promising technique for, for example, manufacturing of miniaturized electronics, and it bridges the gap between top-down and bottom-up methods. However, selecting materials and geometry of the target surface for optimal deposition results presents a significant challenge. Here, we describe a predictive framework based on the Derjaguin–Landau–Verwey–Overbeek theory that allows rational design of colloidal nanoparticle deposition setups. The framework is demonstrated for a model system consisting of gold nanoparticles stabilized by trisodium citrate that are directed toward prefabricated sub-100 nm features on a silicon substrate. Experimental results for the model system are presented in conjunction with theoretical analysis to assess its reliability. It is shown that three-dimensional, nickel-coated structures are well suited for attracting gold nanoparticles and that optimization of the feature geometry based on the proposed framework leads to a systematic improvement in the number of successfully deposited particles.