A role of silica nanoparticles in layer-by-layer self-assembled carbon nanotube and In2O3 nanoparticle thin-film pH sensors: Tunable sensitivity and linearity

Dongjin Lee, Tianhong Cui

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


A role of the dielectric silica nanoparticle (SiO2 NP) in nanomaterial chemoresistors and ion-sensitive field-effect transistors (ISFET) is demonstrated in this study. Single-walled carbon nanotubes (SWCNT) and indium oxide nanoparticles (In2O3 NP) are layer-by-layer self-assembled alternately with oppositely charged polyelectrolytes, respectively. Nanomaterial multilayer thin-film is patterned using photolithography and electrochemically characterized in various pH buffers. The pH sensors are implemented as resistor and transistor in absence and presence of SiO2 NP layer. We observed tunable sensitivity and linearity of output current flowing through the conducting channel in SWCNT chemoresistor and ISFET. The role of SiO2 NP is proven to modulate and linearize the sensitivity to pH. The linearization is attributed to a positive shift in pH gating voltage in p-type semiconducting SWCNTs. On the other hand, a tunable sensitivity is observed whereas the linearization is not demonstrated in In 2O3 NP ISFETs. The increased sensitivity with SiO 2 NP in acidic region is caused by a positive shift in gate voltage due to the protonation of the surface hydroxyl groups. This facile modulation and linearization of the electrochemical sensitivity in semiconducting nanomaterial thin-film device by means of the additional SiO2 NP layer is useful for developing various functional nanomaterial-based biosensors.

Original languageEnglish (US)
Pages (from-to)203-211
Number of pages9
JournalSensors and Actuators, A: Physical
StatePublished - Dec 2012

Bibliographical note

Funding Information:
This work was supported in part by the Defense Advanced Research Projects Agency (DARPA) N/MEMS S&T Fundamentals program under grant no. HR001-06-1-0500 issued to the Micro/nano Fluidics Fundamentals Focus (MF3) Center. The authors would like to acknowledge the Nanofabrication Center and Characterization Facility at the University of Minnesota, which are supported by NSF through NNIN.


  • Carbon nanotube (CNT)
  • Chemoresistor
  • Indium oxide (InO) nanoparticle
  • Silica (SiO) nanoparticle
  • pH sensor


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