Calibration method for a carbon nanotube field-effect transistor biosensor

Multiplexed immunosensing of cancer biomarkers on a split-float-gate graphene transistor microfluidic biochip

This work reports the development of a novel microfluidic biosensor using a graphene field-effect transistor (GFET) design for the parallel label-free analysis of multiple biomarkers. Overcoming the persistent challenge of constructing μm2-sized FET sensitive interfaces that incorporate multiple receptors, we implement a split-float-gate structure that enables the manipulation of multiplexed biochemical functionalization using microfluidic channels. Immunoaffinity biosensing experiments are conducted using the mixture samples containing three liver cancer biomarkers, carcinoembryonic antigen (CEA), α-fetoprotein (AFP), and parathyroid hormone (PTH). The results demonstrate the capability of our label-free biochip to quantitatively detect multiple target biomarkers simultaneously by observing the kinetics in 10 minutes, with the detection limit levels in the nanomolar range. This microfluidic biosensor provides a valuable analytical tool for rapid multi-target biosensing, which can be potentially utilized for domiciliary tests of cancer screening and prognosis, obviating the need for sophisticated instruments and professional operations in hospitals.

Sensing and energy harvesting of fluidic flow by InAs nanowires

Indium arsenide (InAs) nanowire (NW) field effect transistors (FETs) were incorporated into a microfluidic channel to detect the flow rate change as well as to harvest fluid flow energy for electric power generation. Discrete changes in the electric current through InAs NW FETs were observed upon flow rate changes at steps of 1 mL/h (equivalent to ~3 mm/s change in average linear velocity). The current also showed a sign change upon reversing flow direction. By comparing the response of the device with and without a driving voltage between source-drain electrodes, we conclude that the dominant contribution in the response is the streaming potential tuned conductance of NW. In the absence of source-drain voltage, we further demonstrate that the ionic flow could enable generation of an ~mV electrical potential (or ~nA electrical current) inside the InAs NW per mL/h increase of flow rate, most likely due to the charge dragging effect.

Strategies for enhancing the analytical performance of nanomaterial-based sensors

We provide a state-of-the-art review of the main strategies for the enhancement of analytical performance of sensors using nanomaterials, particularly nanowires and carbon-based materials. We emphasize the way to overcome the problem of device-to-device variation. We discuss the study of the influence of nanomaterial characteristics, sensor dimensions and operational conditions on sensing performance, and the application of appropriate calibration models.

Ultrasensitive detection of the reduced form of nicotinamide adenine dinucleotide based on carbon nanotube field effect transistor

We developed a simple, ultrasensitive, and quantitative detection method for the reduced form of nicotinamide adenine dinucleotide (NADH), based on carbon nanotube field effect transistors (CNTFETs). Following the injection of NADH at different concentrations, we obtained different electrical signals from a semiconductor characterization system mimicking biological catalysis of NADH dehydrogenase (CoI). Here, FET was fabricated via photolithography, attaching silicon wells, as the detection chamber, on the channel area of the single wall carbon nanotube (SWCNT). SWCNTs were functionalized with phenazine derivant, a counterpart of the key functional prosthetic group of CoI enzyme. In the presence of NADH, electrons transferred to phenazine derivant through SWCNT, by analogous means of the electron transport chain formed by a series of iron-sulfur (FeS) clusters in CoI. Using this method, the limit of detection was as low as 1 pM, and the range of linear response was 10 pM to 500 nM. Significantly, this approach possesses great potential for applications in real-time detection of NADH at extremely low concentrations, and rigorous analysis for NADH in electrochemical fields.

Universal parameters for carbon nanotube network-based sensors: can nanotube sensors be reproducible?

Carbon nanotube (CNT) network-based sensors have been often considered unsuitable for practical applications due to their unpredictable characteristics. Herein, we report the study of universal parameters which can be used to characterize CNT network-based sensors and make their response predictable. A theoretical model is proposed to explain these parameters, and sensing experiments for mercury (Hg(2+)) and ammonium (NH(4)(+)) ions using CNT network-based sensors were performed to confirm the validity of our model.

A 64-channel readout ASIC for nanowire biosensor array with electrical calibration scheme

A 1.8-mW, 18.5-mm(2) 64-channel current readout ASIC was implemented in 0.18-µm CMOS together with a new calibration scheme for silicon nanowire biosensor arrays. The ASIC consists of 64 channels of dedicated readout and conditioning circuits which incorporate correlated double sampling scheme to reduce the effect of 1/f noise and offset from the analog front-end. The ASIC provides a 10-bit digital output with a sampling rate of 300 S/s whilst achieving a minimum resolution of 7 pA(rms). A new electrical calibration method was introduced to mitigate the issue of large variations in the nano-scale sensor device parameters and optimize the sensor sensitivity. The experimental results show that the proposed calibration technique improved the sensitivity by 2 to 10 times and reduced the variation between dataset by 9 times.

A calibration method for nanowire biosensors to suppress device-to-device variation

Nanowire/nanotube biosensors have stimulated significant interest; however, the inevitable device-to-device variation in the biosensor performance remains a great challenge. We have developed an analytical method to calibrate nanowire biosensor responses that can suppress the device-to-device variation in sensing response significantly. The method is based on our discovery of a strong correlation between the biosensor gate dependence (dI(ds)/dV(g)) and the absolute response (absolute change in current, DeltaI). In(2)O(3) nanowire-based biosensors for streptavidin detection were used as the model system. Studying the liquid gate effect and ionic concentration dependence of strepavidin sensing indicates that electrostatic interaction is the dominant mechanism for sensing response. Based on this sensing mechanism and transistor physics, a linear correlation between the absolute sensor response (DeltaI) and the gate dependence (dI(ds)/dV(g)) is predicted and confirmed experimentally. Using this correlation, a calibration method was developed where the absolute response is divided by dI(ds)/dV(g) for each device, and the calibrated responses from different devices behaved almost identically. Compared to the common normalization method (normalization of the conductance/resistance/current by the initial value), this calibration method was proven advantageous using a conventional transistor model. The method presented here substantially suppresses device-to-device variation, allowing the use of nanosensors in large arrays.

Electrolyte-gated graphene field-effect transistors for detecting pH and protein adsorption

We investigated electrolyte-gated graphene field-effect transistors (GFETs) for electrical detecting pH and protein adsorptions. Nonfunctionalized single-layer graphene was used as a channel. GFETs immersed in an electrolyte showed transconductances 30 times higher than those in a vacuum and their conductances exhibited a direct linear increase with electrolyte pH, indicating their potential for use in pH sensor applications. We also attempted to direct surface-protein adsorption and showed that the conductance of GFETs increased with exposure to a protein at several hundred picomolar. The GFETs thus acted as highly sensitive electrical sensors for detecting pH and biomolecule concentrations.

Recent advances in nanotechnology applied to biosensors

In recent years there has been great progress the application of nanomaterials in biosensors. The importance of these to the fundamental development of biosensors has been recognized. In particular, nanomaterials such as gold nanoparticles, carbon nanotubes, magnetic nanoparticles and quantum dots have been being actively investigated for their applications in biosensors, which have become a new interdisciplinary frontier between biological detection and material science. Here we review some of the main advances in this field over the past few years, explore the application prospects, and discuss the issues, approaches, and challenges, with the aim of stimulating a broader interest in developing nanomaterial-based biosensors and improving their applications in disease diagnosis and food safety examination.