The pH Sensing Characteristics of the Extended-Gate Field-Effect Transistors of Multi-Walled Carbon-Nanotube Thin Film Using Low-Temperature Ultrasonic Spray Method

Abstract

A novel, simple and low-temperature ultrasonic spray method was developed to fabricate the multi-walled carbon-nanotubes (MWCNTs) based extended-gate field-effect transistors (EGFETs) as the pH sensor. With an acid-treated process, the chemically functionalized two-dimensional MWCNT network could provide plenty of functional groups which exhibit hydrophilic property and serve as hydrogen sensing sites. For the first time, the EGFET using a MWCNT structure could achieve a wide sensing rage from pH = 1 to pH = 13. Furthermore, the pH sensitivity and linearity values of the CNT pH-EGFET devices were enhanced to 51.74 mV/pH and 0.9948 from pH = 1 to pH = 13 while the sprayed deposition reached 50 times. The sensing properties of hydrogen and hydroxyl ions show significantly dependent on the sprayed deposition times, morphologies, crystalline and chemical bonding of acid-treated MWCNT. These results demonstrate that the MWCNT-EGFETs are very promising for the applications in the pH and biomedical sensors.

The use of a multiple roughening scheme to enhance sensing performance of pH sensors with NiO nanosheets/multi-walled carbon nanotubes on KOH-etched Si substrates

“…[56][57][58] The G-band (∼1580 cm −1 ) of single crystal hexagonal graphite can be ascribed to the sp 2 C=C bond stretching motions in CNTs. 23,59) The D′ band (∼1620 cm −1 ) is a dual-resonance Raman feature induced by disorder and defects. 60) The R value with regard to the ratio of the D band and G band intensities, I(D)/I(G), is a very significant factor to identify the structural imperfections, i.e.…”

“…Therefore, EGFET reveals many advantages over the conventional ISFET with low cost, simple to package with the FET isolated from its chemical environment, flexible shape of the extended-gate structure, and good long-term stability. [10][11][12] Recently, pH SEs using nanostructured materials such as zinc oxide (ZnO) based materials, 10,13,14) titanium oxide (TiO 2 ), [15][16][17] tin oxide (SnO 2 ), 18) vanadium pentoxide (V 2 O 5 ), 19,20) tungsten oxide (WO 3 ), 21,22) multi-walled carbon nanotube (MWCNT), [23][24][25][26][27] nickel oxide (NiO), 28,29) etc., to enhance the sensitivity of pH sensors was demonstrated. It shows that the increase in the amount of ion adsorption sites through increasing the surface area (SA) of metal oxides and MWCNT nanostructures, in addition to the material itself, is very beneficial for ion sensing.…”

Functionalized Carbon Nanotube Thin Films as the pH Sensing Membranes of Extended-Gate Field-Effect Transistors on the Flexible Substrates

“…Recently, carbon-related materials, including graphene [16]- [18] and carbon nanotube (CNT) [19], have been regarded as the promising sensing materials since they possess great electrical properties, outstanding mechanical strength, and good chemical inertness. The epitaxial graphene FET was used in an aqueous environment as a pH sensor in 2008 [17] and then the platform of graphene FET has been mainly fabricated and studied for pH sensing.…”

High Density Horizontal-aligned Carbon Nanotube Thin Film with Oxygen Plasma Treatment as pH Sensing Membrane of Extended-Gate Field-Effect Transistor

“…Therefore, EGFETs are an alternative to conventional ISFETs with lower cost, less sensitivity to the environment, simpler packaging, and better long-term stability [2]. Recently, carbon nanotube thin films (CNTFs) have been proposed as a promising pH-sensing membrane for EGFETs [3] because they possess high mechanical strength, high surface-to-volume ratio, good electrical conductivity, and high chemical inertness. However, to date, CNTFs have been mingled with polymer [4] or metal [5] to improve the pH sensing characteristics of pristine CNTFs.…”