Peptide aptamer-modified single-walled carbon nanotube-based transistors for high-performance biosensors

Abstract

Biosensors employing single-walled carbon nanotube field-effect transistors (SWCNT FETs) offer ultimate sensitivity. However, besides the sensitivity, a high selectivity is critically important to distinguish the true signal from interference signals in a non-controlled environment. This work presents the first demonstration of the successful integration of a novel peptide aptamer with a liquid-gated SWCNT FET to achieve highly sensitive and specific detection of Cathepsin E (CatE), a useful prognostic biomarker for cancer diagnosis. Novel peptide aptamers that specifically recognize CatE are engineered by systemic in vitro evolution. The SWCNTs were firstly grown using the thermal chemical vapor deposition (CVD) method and then were employed as a channel to fabricate a SWCNT FET device. Next, the SWCNTs were functionalized by noncovalent immobilization of the peptide aptamer using 1-pyrenebutanoic acid succinimidyl ester (PBASE) linker. The resulting FET sensors exhibited a high selectivity (no response to bovine serum albumin and cathepsin K) and label-free detection of CatE at unprecedentedly low concentrations in both phosphate-buffered saline (2.3 pM) and human serum (0.23 nM). Our results highlight the use of peptide aptamer-modified SWCNT FET sensors as a promising platform for near-patient testing and point-of-care testing applications.

Figure 1

Schematic of the concept. The integration of a novel peptide aptamer with a SWCNT FET to achieve highly selective and sensitive biosensing of unreached biomarkers.

Figure 2

Device fabrication and characterization. (a) SEM image of a fabricated SWCNT FET (white arrow indicates the SWCNT) and real image of a fabricated chip, which contains an array of 52 SWCNT FETs; (b) Raman spectra of an as-grown SWCNT and the substrate (black arrow indicates the characteristic RBM of the SWCNT); and (c) transfer characteristics of the fabricated SWCNT FET.

Figure 3

Peptide aptamer characterization. (a) The sequence and predicted structure of the selected peptide aptamer; and (b) SPR analysis for the affinity binding of the peptide aptamer to Cathepsin E using single-cycle mode with an aptamer level of 1000 RU and sequential injections of five ascending concentrations of analyte Cathepsin E (858.37, 171.67, 34.33, 6.87, 1.37 ng/mL). The data for the steady-state affinity binding plot were calculated from the end of the association phases against the analyte concentration.

Figure 4

Schematic of the experimental setup. The immobilization of the peptide aptamer onto the surface of a SWCNT and the operating setup of the liquid-gated SWCNT FET device for CatE detection.

Figure 5

Quantitative detection of CatE in phosphate-buffered saline. (a) Transfer characteristics of the peptide aptamer-modified SWCNT FET for various CatE concentrations. (b) The relative decrease in the “on” current (∆I/∆I_max) as a function of the CatE concentration. The inset shows the CatE concentration/(∆I/∆I_max) as a function of CatE concentration. (c) Transfer characteristics of the PBASE-modified SWCNT FET without the peptide aptamer for 1 ng/mL CatE. The inset shows the comparison of the SWCNT FETs with and without peptide aptamers responding to 1 ng/mL CatE. Transfer characteristics of the peptide aptamer-modified SWCNT FET for 1 ng/mL BSA (d) and 0.1 and 1 ng/mL CatK (e). (f) The relative change in “on” current (∆I/I_o) versus concentration was plotted for CatE, BSA and CatK.

Figure 6

Quantitative detection of CatE in human serum. (a) Transfer characteristics of the peptide aptamer-modified SWCNT FET for various CatE concentrations in 10-fold-diluted human serum. (b) The relative decrease in “on” current (∆I/∆I_max) as a function of CatE concentration.