Detection of ultra-low protein concentrations with the simplest possible field effect transistor

Silicon nanowire (Si NW) sensors have attracted great attention due to their ability to provide fast, low-cost, label-free, real-time detection of chemical and biological species. Usually configured as field effect transistors (FETs), they have already demonstrated remarkable sensitivity with high selectivity (through appropriate functionalisation) towards a large number of analytes in both liquid and gas phases. Despite these excellent results, Si NW FET sensors have not yet been successfully employed to detect single molecules of either a chemical or biological target species. Here we show that sensors based on silicon junctionless nanowire transistors (JNTs), the simplest possible transistors, are capable of detecting the protein streptavidin at a concentration as low as 580 zM closely approaching the single molecule level. This ultrahigh detection sensitivity is due to the intrinsic advantages of junctionless devices over conventional FETs. Apart from their superior functionality, JNTs are much easier to fabricate by standard microelectronic processes than transistors containing p–n junctions. The ability of JNT sensors to detect ultra-low concentrations (in the zeptomolar range) of target species, and their potential for low-cost mass production, will permit their deployment in numerous environments, including life sciences, biotechnology, medicine, pharmacology, product safety, environmental monitoring and security

A miniaturised autonomous sensor based on nanowire materials platform: the SiNAPS mote

A micro-power energy harvesting system based on core(crystalline Si)-shell(amorphous Si) nanowire solar cells together with a nanowire-modified CMOS sensing platform have been developed to be used in a dust-sized autonomous chemical sensor node. The mote (SiNAPS) is augmented by low-power electronics for power management and sensor interfacing, on a chip area of 0.25mm2. Direct charging of the target battery (e.g., NiMH microbattery) is achieved with end-to-end efficiencies up to 90% at AM1.5 illumination and 80% under 100 times reduced intensity. This requires matching the voltages of the photovoltaic module and the battery circumventing maximum power point tracking. Single solar cells show efficiencies up to 10% under AM1.5 illumination and open circuit voltages, Voc, of 450-500mV. To match the battery’s voltage the miniaturised solar cells (~1mm2 area) are connected in series via wire bonding. The chemical sensor platform (mm2 area) is set up to detect hydrogen gas concentration in the low ppm range and over a broad temperature range using a low power sensing interface circuit. Using Telran TZ1053 radio to send one sample measurement of both temperature and H2 concentration every 15 seconds, the average and active power consumption for the SiNAPS mote are less than 350nW and 2.1 μW respectively. Low-power miniaturised chemical sensors of liquid analytes through microfluidic delivery to silicon nanowires are also presented. These components demonstrate the potential of further miniaturization and application of sensor nodes beyond the typical physical sensors, and are enabled by the nanowire materials platform

Mid-rapidity anti-proton to proton ratio from Au+Au collisions at sNN=130 \sqrt{s_{NN}} = 130 GeV

We report results on the ratio of mid-rapidity anti-proton to proton yields in Au+Au collisions at \rts = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of $|y|<0.5$ and 0.4 $<p_t<$ 1.0 GeV/$c$, the ratio is essentially independent of either transverse momentum or rapidity, with an average of $0.65\pm 0.01_{\rm (stat.)} \pm 0.07_{\rm (syst.)}$ for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the $p$-\pb pair production becomes important at mid-rapidity, a significant excess of baryons over anti-baryons is still present.Comment: 5 pages, 3 figures, accepted by Phys. Rev. Let

Nanocrystal synthesis in microfluidic reactors: Where next?

The past decade has seen a steady rise in the use of microfluidic reactors for nanocrystal synthesis, with numerous studies reporting improved reaction control relative to conventional batch chemistry. However, flow synthesis procedures continue to lag behind batch methods in terms of chemical sophistication and the range of accessible materials, with most reports having involved simple one- or two-step chemical procedures directly adapted from proven batch protocols. Here we examine the current status of microscale methods for nanocrystal synthesis, and consider what role microreactors might ultimately play in laboratory-scale research and industrial production.ISSN:1473-0197ISSN:1473-018

Sub-15-nm patterning of asymmetric metal electrodes and devices by adhesion lithography

Coplanar electrodes formed from asymmetric metals separated on the nanometre length scale are essential elements of nanoscale photonic and electronic devices. Existing fabrication methods typically involve electron-beam lithography—a technique that enables high fidelity patterning but suffers from significant limitations in terms of low throughput, poor scalability to large areas and restrictive choice of substrate and electrode materials. Here, we describe a versatile method for the rapid fabrication of asymmetric nanogap electrodes that exploits the ability of selected self-assembled monolayers to attach conformally to a prepatterned metal layer and thereby weaken adhesion to a subsequently deposited metal film. The method may be carried out under ambient conditions using simple equipment and a minimum of processing steps, enabling the rapid fabrication of nanogap electrodes and optoelectronic devices with aspect ratios in excess of 100,000

Large-scale synthesis of nanocrystals in a multichannel droplet reactor

We report a multichannel microfluidic droplet reactor for the large-scale, high temperature synthesis of nanocrystals. The reactor was applied here to the production of CdTe, CdSe and alloyed CdSeTe nanocrystals, and found in all cases to provide high quality quantum dots with spectral properties that did not vary between channels or over time. One hour test runs yielded 3.7, 1.5 and 2.1 g of purified CdTe, CdSe and the alloy, respectively, using 0.4 M cadmium precursor solutions and carrier and reagent phase flow rates of 4 and 2 ml min−1. A further nine hour test-run applied to CdTe, utilizing increased carrier and reagent flow rates of 5 and 3 ml min−1, yielded 54.4 g of dry purified material, corresponding to a production rate of 145 g per day. The reactor architecture is inherently scalable and, with only minimal modifications, should allow for straightforward expansion to the kilogram-per-day production levels sought by industry

Fully CMOS-compatible top-down fabrication of sub-50 nm silicon nanowire sensing devices

This article reports the fabrication of sub-50 nm field effect transistor (FET)-type silicon (Si) nanowire (Si NW) chemical and biological sensing devices with a junctionless architecture, as well as on the initial characterisation of their electrical and sensing performance. The devices were fabricated using a fully complementary metal-oxide-semiconductor (CMOS)-compatible top-down process on silicon-on-insulator (SOI) wafers. The fabrication process was mainly based on high-resolution electron beam lithography (EBL) and reactive ion etching (RIE) but also included photolithography (mix-and-match lithography), thin film deposition by electron beam evaporation, lift-off, thermal annealing and wet etching. The sensing performance of a matrix of nanowire devices, i.e. containing 1, 3 and 20 NWs with lengths of 0.5, 1 and 10 μm was examined. Each element of the matrix also contained five devices with different NW widths: 10, 20, 30, and 50 nm and 5 μm (a Si belt reference device). Electrical characterisation of the devices showed excellent performance as backgated junctionless nanowire transistors (JNTs): high on-currents in the range of 1-10 μA and high ratios between the on-state and off-state currents (I on/Ioff) of 6-7 orders of magnitude. In addition, the results of ionic strength sensing experiments demonstrate the very good sensing capabilities of these devices. To the best of our knowledge, these nanowire sensors are among the smallest top-down fabricated Si NW devices reported to date