Time-dependent pH sensing phenomena using CdSe/ZnS quantum dots in EIS structure.

Pankaj Kumar,Ta-Chang Tien,Siddheswar Maikap,Amit Prakash

doi:10.1186/1556-276x-9-179

Abstract

Time-dependent pH sensing phenomena of the core-shell CdSe/ZnS quantum dot (QD) sensors in EIS (electrolyte insulator semiconductor) structure have been investigated for the first time. The quantum dots are immobilized by chaperonin GroEL protein, which are observed by both atomic force microscope and scanning electron microscope. The diameter of one QD is approximately 6.5 nm. The QDs are not oxidized over a long time and core-shell CdSe/ZnS are confirmed by X-ray photon spectroscopy. The sensors are studied for sensing of hydrogen ions concentration in different buffer solutions at broad pH range of 2 to 12. The QD sensors show improved sensitivity (38 to 55 mV/pH) as compared to bare SiO2 sensor (36 to 23 mV/pH) with time period of 0 to 24 months, owing to the reduction of defects in the QDs. Therefore, the differential sensitivity of the QD sensors with respect to the bare SiO2 sensors is improved from 2 to 32 mV/pH for the time period of 0 to 24 months. After 24 months, the sensitivity of the QD sensors is close to ideal Nernstian response with good linearity of 99.96%. Stability and repeatability of the QD sensors show low drift (10 mV for 10 cycles) as well as small hysteresis characteristics (<10 mV). This QD sensor is very useful for future human disease diagnostics.

Highlights

Among the numerous chemical sensors, pH sensor is the major field of research area, which is one of the controlled parameter for the biochemical industrial processes
The distribution of the quantum dot (QD) on chaperonin protein layer attached on SiO2 surface (Figure 4a) and very few QDs appear on the surface, as most of the QDs have been attached at both side and the bottom of protein via ZnS-thiol group interaction at cysteine amino acid
The CdSe/ZnS QDs in electrolyte insulator semiconductor (EIS) structure have been successfully immobilized on SiO2 film using chaperonin protein

Summary

Introduction

Among the numerous chemical sensors, pH sensor is the major field of research area, which is one of the controlled parameter for the biochemical industrial processes. Nanoparticles have generated considerable interest as diagnostic tool because of their small sizes and comparatively higher surface area that leads to more interaction with ions in solution [7,8,9,10]. Semiconductor nanoparticles such as quantum dots (QDs) are one of the major candidates being properties using different nanoparticles, time-dependent improved pH sensitivity using CdSe/ZnS QDs has not yet been reported

Methods

Results

Conclusion