Direct Electrical Readout Research Articles

Top-down nanofabrication of silicon nanoribbon field effect transistor (Si-NR FET) for carcinoembryonic antigen detection.

Sensitive and quantitative detection of tumor markers is highly required in the clinic for cancer diagnosis and consequent treatment. A field-effect transistor-based (FET-based) nanobiosensor emerges with characteristics of being label-free, real-time, having high sensitivity, and providing direct electrical readout for detection of biomarkers. In this paper, a top–down approach is proposed and implemented to fulfill a novel silicon nano-ribbon FET, which acts as biomarker sensor for future clinical application. Compared with the bottom–up approach, a top–down fabrication approach can confine width and length of the silicon FET precisely to control its electrical properties. The silicon nanoribbon (Si-NR) transistor is fabricated on a Silicon-on-Insulator (SOI) substrate by a top–down approach with complementary metal oxide semiconductor (CMOS)-compatible technology. After the preparation, the surface of Si-NR is functionalized with 3-aminopropyltriethoxysilane (APTES). Glutaraldehyde is utilized to bind the amino terminals of APTES and antibody on the surface. Finally, a microfluidic channel is integrated on the top of the device, acting as a flowing channel for the carcinoembryonic antigen (CEA) solution. The Si-NR FET is 120 nm in width and 25 nm in height, with ambipolar electrical characteristics. A logarithmic relationship between the changing ratio of the current and the CEA concentration is measured in the range of 0.1–100 ng/mL. The sensitivity of detection is measured as 10 pg/mL. The top–down fabricated biochip shows feasibility in direct detecting of CEA with the benefits of real-time, low cost, and high sensitivity as a promising biosensor for tumor early diagnosis.

Plasmonic Sensor Monolithically Integrated with a CMOS Photodiode

Complementary metal oxide semiconductor (CMOS) technology has made personal mobile computing and communications an everyday part of life. In this paper we present a nanophotonic integrated CMOS-based biosensor that will pave the way for future personalized medical diagnostics. To achieve our aim, we have monolithically integrated plasmonic nanostructures with a CMOS photodiode. Following this approach of monolithic nanophotonics–microelectronics integration, we have successfully developed a miniaturized nanophotonic sensor system with direct electrical readout, which eliminates the need of bulky and costly equipment that is presently used for interrogation of nanophotonic sensors. The optical sensitivity of the plasmonic nanostructures is measured to be 275 nm/refractive index unit (RIU), which translates to an electrical sensitivity of 5.8 V/RIU in our integrated sensor system. This advance is the first demonstration of monolithic integration of nanophotonic structures with CMOS detectors and is a crucia...

Progress in Silicon Nanowire‐Based Field‐Effect Transistor Biosensors for Label‐Free Detection of DNA

AbstractSilicon nanowire (SiNW), as one‐dimensional semiconducting nanomaterial, has been incorporated into the filed‐effect transistor (FET) devices to increase the efficacy and signal‐to‐noise in DNA sensing applications. Due to the advantages of high sensitivity, excellent selectivity, label‐free detection, direct electrical readout, and miniaturization, SiNW FET‐based DNA sensors have been regarded as an important tool in applications of molecular diagnostics, DNA sequencing, gene expressions, and drug discovery. Here, we review the recent progress in SiNW‐FET sensors for label‐free electrical DNA detection. We first introduce the working principle of SiNW‐FET DNA sensors, SiNW fabrication technologies, bio‐functionalization on nanowire surface, and enhancement of device sensitivity. Then we sum up the applications of SiNW sensors in detection of DNA hybridization, infectious viruses, microRNA, genetic change (DNA mutation, DNA methylation, and DNA repair), and protein‐DNA interactions. We address several crucial points of sensing performance including sensitivity, selectivity, and limit of detection. Finally, the perspectives, challenges, and some solutions of the field are also discussed.

Conducting polymer based electrochemical biosensors

Conducting polymer (CP)-based electrochemical biosensors have gained great attention as such biosensor platforms are easy and cost-effective to fabricate, and provide a direct electrical readout for the presence of biological analytes with high sensitivity and selectivity. CP materials themselves are both sensing elements and transducers of the biological recognition event at the same time, simplifying sensor designs. This review summarizes the advances in electrochemical biosensors based on CPs. Recognition probe immobilisation techniques, transduction mechanisms and detection of various target biomolecules have been discussed in detail. Efforts to miniaturize CP-based electrochemical biosensors and fabrication of sensor arrays are also briefly reviewed.

Label-free detection of DNA using a light-addressable potentiometric sensor modified with a positively charged polyelectrolyte layer.

A multi-spot (16 spots) light-addressable potentiometric sensor (MLAPS) consisting of an Al-p-Si-SiO2 structure modified with a weak polyelectrolyte layer of PAH (poly(allylamine hydrochloride)) was applied for the label-free electrical detection of DNA (deoxyribonucleic acid) immobilization and hybridization by the intrinsic molecular charge for the first time. To achieve a preferentially flat orientation of DNA strands and thus, to reduce the distance between the DNA charge and MLAPS surface, the negatively charged probe single-stranded DNAs (ssDNA) were electrostatically adsorbed onto the positively charged PAH layer using a simple layer-by-layer (LbL) technique. In this way, more DNA charge can be positioned within the Debye length, yielding a higher sensor signal. The surface potential changes in each spot induced due to the surface modification steps (PAH adsorption, probe ssDNA immobilization, hybridization with complementary target DNA (cDNA), non-specific adsorption of mismatched ssDNA) were determined from the shifts of photocurrent-voltage curves along the voltage axis. A high sensor signal of 83 mV was registered after immobilization of probe ssDNA onto the PAH layer. The hybridization signal increases from 5 mV to 32 mV with increasing the concentration of cDNA from 0.1 nM to 5 μM. In contrast, a small signal of 5 mV was recorded in the case of non-specific adsorption of fully mismatched ssDNA (5 μM). The obtained results demonstrate the potential of the MLAPS in combination with the simple and rapid LbL immobilization technique as a promising platform for the future development of multi-spot light-addressable label-free DNA chips with direct electrical readout.

Resistive graphene humidity sensors with rapid and direct electrical readout.

We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N2), oxygen (O2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO2 substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.

Gating capacitive field-effect sensors by the charge of nanoparticle/molecule hybrids.

The semiconductor field-effect platform is a powerful tool for chemical and biological sensing with direct electrical readout. In this work, the field-effect capacitive electrolyte-insulator-semiconductor (EIS) structure - the simplest field-effect (bio-)chemical sensor - modified with citrate-capped gold nanoparticles (AuNPs) has been applied for a label-free electrostatic detection of charged molecules by their intrinsic molecular charge. The EIS sensor detects the charge changes in AuNP/molecule inorganic/organic hybrids induced by the molecular adsorption or binding events. The feasibility of the proposed detection scheme has been exemplarily demonstrated by realizing capacitive EIS sensors consisting of an Al-p-Si-SiO2-silane-AuNP structure for the label-free detection of positively charged cytochrome c and poly-d-lysine molecules as well as for monitoring the layer-by-layer formation of polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4-styrene sulfonate), representing typical model examples of detecting small proteins and macromolecules and the consecutive adsorption of positively/negatively charged polyelectrolytes, respectively. For comparison, EIS sensors without AuNPs have been investigated, too. The adsorption of molecules on the surface of AuNPs has been verified via the X-ray photoelectron spectroscopy method. In addition, a theoretical model of the functioning of the capacitive field-effect EIS sensor functionalized with AuNP/charged-molecule hybrids has been discussed.

A Back-Gate Controlled Silicon Nanowire Sensor with Sensitivity Improvement for DNA and pH Detection

Silicon nanowire field-effect transistors (SiNW-FETs) are emerging as powerful chemical and biological sensors with various attractive features including high sensitivity and direct electrical readout. However, limited systematic studies have appeared on how the working voltage affects their sensitivity. Here we demonstrate that the current change rate of SiNW-FETs can be exponentially enhanced in the subthreshold regime by both analyses of FET's theory model and electrical characteristics. On that basis, the back-gate controlled sensors' detection sensitivity for DNA and pH value appears great improvement when working in the subthreshold regime, which shows that optimization of SiNW-FET operating conditions, can provide significant improvement for the limits of SiNW-FET nanosensors, making it possible for higher-accuracy chemical and biological molecules detection.

Silicon-based optoelectronic integrated circuit for label-free bio/chemical sensor

We demonstrate a silicon-based optoelectronic integrated circuit (OEIC) for label-free bio/chemical sensing application. Such on-chip OEIC sensor system consists of optical grating couplers for vertical light coupling into silicon waveguides, a thermal-tunable microring as a tunable filter, an exposed microring as an optical label-free sensor, and a Ge photodetector for a direct electrical readout. Different from the conventional wavelength-scanning method, we adopt low-cost broadband ASE light source, together with the on-chip tunable filter to generate sliced light source. The effective refractive index change of the sensing microring induced by the sensing target is traced by scanning the supplied electrical power applied onto the tracing microring, and the detected electrical signal is read out by the Ge photodetector. For bulk refractive index sensing, we demonstrate using such OEIC sensing system with a sensitivity of ~15 mW/RIU and a detection limit of 3.9 μ-RIU, while for surface sensing of biotin-streptavidin, we obtain a surface mass sensitivity of S(m) = ~192 µW/ng·mm(-2) and a surface detection limit of 0.3 pg/mm(2). The presented OEIC sensing system is suitable for point-of-care applications.

Electromechanical Piezoresistive Sensing in Suspended Graphene Membranes

Monolayer graphene exhibits exceptional electronic and mechanical properties, making it a very promising material for nanoelectromechanical devices. Here, we conclusively demonstrate the piezoresistive effect in graphene in a nanoelectromechanical membrane configuration that provides direct electrical readout of pressure to strain transduction. This makes it highly relevant for an important class of nanoelectromechanical system (NEMS) transducers. This demonstration is consistent with our simulations and previously reported gauge factors and simulation values. The membrane in our experiment acts as a strain gauge independent of crystallographic orientation and allows for aggressive size scalability. When compared with conventional pressure sensors, the sensors have orders of magnitude higher sensitivity per unit area.

Electrical monitoring of polyelectrolyte multilayer formation by means of capacitive field-effect devices

The semiconductor field-effect platform represents a powerful tool for detecting the adsorption and binding of charged macromolecules with direct electrical readout. In this work, a capacitive electrolyte-insulator-semiconductor (EIS) field-effect sensor consisting of an Al-p-Si-SiO2 structure has been applied for real-time in situ electrical monitoring of the layer-by-layer formation of polyelectrolyte (PE) multilayers (PEM). The PEMs were deposited directly onto the SiO2 surface without any precursor layer or drying procedures. Anionic poly(sodium 4-styrene sulfonate) and cationic weak polyelectrolyte poly(allylamine hydrochloride) have been chosen as a model system. The effect of the ionic strength of the solution, polyelectrolyte concentration, number and polarity of the PE layers on the characteristics of the PEM-modified EIS sensors have been studied by means of capacitance-voltage and constant-capacitance methods. In addition, the thickness, surface morphology, roughness and wettabilityof the PE mono- and multilayers have been characterised by ellipsometry, atomic force microscopy and water contact-angle methods, respectively. To explain potential oscillations on the gate surface and signal behaviour of the capacitive field-effect EIS sensor modified with a PEM, a simplified electrostatic model that takes into account the reduced electrostatic screening of PE charges by mobile ions within the PEM has been proposed and discussed.

Narrowband photodetection in the near-infrared with a plasmon-induced hot electron device

In gratings, incident light can couple strongly to plasmons propagating through periodically spaced slits in a metal film, resulting in a strong, resonant absorption whose frequency is determined by the nanostructure periodicity. When a grating is patterned on a silicon substrate, the absorption response can be combined with plasmon-induced hot electron photocurrent generation. This yields a photodetector with a strongly resonant, narrowband photocurrent response in the infrared, limited at low frequencies by the Schottky barrier, not the bandgap of silicon. Here we report a grating-based hot electron device with significantly larger photocurrent responsivity than previously reported antenna-based geometries. The grating geometry also enables more than three times narrower spectral response than observed for nanoantenna-based devices. This approach opens up the possibility of plasmonic sensors with direct electrical readout, such as an on-chip surface plasmon resonance detector driven at a single wavelength.

Enhanced Sensing of Nucleic Acids with Silicon Nanowire Field Effect Transistor Biosensors

Silicon nanowire (SiNW) field effect transistors (FETs) have emerged as powerful sensors for ultrasensitive, direct electrical readout, and label-free biological/chemical detection. The sensing mechanism of SiNW-FET can be understood in terms of the change in charge density at the SiNW surface after hybridization. So far, there have been limited systematic studies on fundamental factors related to device sensitivity to further make clear the overall effect on sensing sensitivity. Here, we present an analytical result for our triangle cross-section wire for predicting the sensitivity of nanowire surface-charge sensors. It was confirmed through sensing experiments that the back-gated SiNW-FET sensor had the highest percentage current response in the subthreshold regime and the sensor performance could be optimized in low buffer ionic strength and at moderate probe concentration. The optimized SiNW-FET nanosensor revealed ultrahigh sensitivity for rapid and reliable detection of target DNA with a detection limit of 0.1 fM and high specificity for single-nucleotide polymorphism discrimination. In our work, enhanced sensing of biological species by optimization of operating parameters and fundamental understanding for SiNW FET detection limit was obtained.

Plasmon Resonance in Individual Nanogap Electrodes Studied Using Graphene Nanoconstrictions as Photodetectors

We achieve direct electrical readout of the wavelength and polarization dependence of the plasmon resonance in individual gold nanogap antennas by positioning a graphene nanoconstriction within the gap as a localized photodetector. The polarization sensitivities can be as large as 99%, while the plasmon-induced photocurrent enhancement is 2-100. The plasmon peak frequency, polarization sensitivity, and photocurrent enhancement all vary between devices, indicating the degree to which the plasmon resonance is sensitive to nanometer-scale irregularities.

Analysis of Field-Effect Biosensors using Self-Consistent 3D Drift-Diffusion and Monte-Carlo Simulations

Field-effect biosensors based on nanowires enjoy considerable popularity due to their high sensitivity and direct electrical readout [1]. However, crucial issues such as the influence of the biomolecules on the charge-carrier transport or the binding of molecules to the surface have not been described satisfactorily yet in a quantitative manner. In order to analyze these effects, we present simulation results based on a 3D macroscopic transport model coupled with Monte-Carlo simulations for the bio-functionalized surface layer. Excellent agreement with measurement data has been found, while detailed study of the influence of the most prominent biomolecules, namely double-stranded DNA and single-stranded DNA, on the current through the semiconductor transducer has been carried out.

Subthreshold Regime has the Optimal Sensitivity for Nanowire FET Biosensors

Nanowire field-effect transistors (NW-FETs) are emerging as powerful sensors for detection of chemical/biological species with various attractive features including high sensitivity and direct electrical readout. Yet to date there have been limited systematic studies addressing how the fundamental factors of devices affect their sensitivity. Here we demonstrate that the sensitivity of NW-FET sensors can be exponentially enhanced in the subthreshold regime where the gating effect of molecules bound on a surface is the most effective due to the reduced screening of carriers in NWs. This principle is exemplified in both pH and protein sensing experiments where the operational mode of NW-FET biosensors was tuned by electrolyte gating. The lowest charge detectable by NW-FET sensors working under different operational modes is also estimated. Our work shows that optimization of NW-FET structure and operating conditions can provide significant enhancement and fundamental understanding for the sensitivity limits of NW-FET sensors.

A thermal sensor and switch based on a plasma polymer/ZnO suspended nanobelt bimorphstructure

The combination of design and subsequent fabrication of organic/inorganic nanostructurescreates an effective way to combine the favorable traits of both to achieve a desired deviceperformance. We demonstrate a miniature electrical read-out, and a sensitive temperaturesensor/switch, based on a ZnO nanobelt/plasma-polymerized benzonitrile bimorphstructure. A new read-out technique based on the change in the electric current flowingthrough the bimorph and the contact pad has been employed, replacing the conventionalcumbersome piezoresistive method or tedious optical alignment. The thermal sensordemonstrated here has great prospects for thermal switching and triggered detectionowing to the relative ease in the fabrication of arrays and the direct electricalread-out.

Sequence specific electronic conduction through polyion-stabilized double-stranded DNA innanoscale break junctions

This paper presents a study of sequence specific electronic conduction through short(15-base-pair) double-stranded (ds) DNA molecules, measured by immobilizing3′-thiol-derivatized DNAs in nanometre scale gaps between gold electrodes. The polycationspermidine was used to stabilize the ds-DNA structure, allowing electrical measurements tobe performed in a dry state. For specific sequences, the conductivity was observed to scalewith the surface density of immobilized DNA, which can be controlled by the bufferconcentration. A series of 15-base DNA oligonucleotide pairs, in which the centresequence of five base pairs was changed from G:C to A:T pairs, has been studied.The conductivity per molecule is observed to decrease exponentially with thenumber of adjacent A:T pairs replacing G:C pairs, consistent with a barrier at theA:T sites. Conductance-based devices for short DNA sequences could providesensing approaches with direct electrical readout, as well as label-free detection.

Towards Label-free Detection of Charged Macromolecules Using Field-effect-based Structures: Scaling Down from Capacitive EIS Sensor over ISFET to Nano-scale Devices

AbstractThe possibility of a label-free electrical detection of charged macromolecules using semiconductor field-effect sensors offers a new approach for the development of DNA chips with fast and direct electrical readout. A deep understanding of the adsorption and interaction of charged biomolecules onto charged surfaces is of great interest also for the fundamental understanding of many key physiological processes. In the present work, two types of field-effect sensors, namely a capacitive EIS (electrolyte-insulator-semiconductor) structure and an ISFET (ion-sensitive field-effect transistor) have been utilised for monitoring layer-by-layer adsorption of polyelectrolytes as well as for the DNA immobilisation and hybridisation detection.

DNA sensor based on functionalized polypyrrole

A novel DNA sensor based on a functionalized polypyrrole was prepared. The sensor film was obtained by electrocopolymerizing poly(pyrrole- co-4-(3-pyrrolyl) butanoic acid) onto which an NH 2-ODN probe was grafted. The obtained sensor is a simple, label-free DNA sensor with direct electrical read-out. Hybridisation with complementary ODN was investigated by observing changes in die cyclic voltammogram and the AC impedance spectrum. Significant modifications of both the voltammogram and AC impedance spectrum were observed when the sensor was incubated in the presence of complementary ODN. The AC impedance spectra show an increased charge transfer resistance of the film after hybridisation.