Bode Phase Angle Signaling of a TB Disease Biomarker

Abstract

Tuberculosis (TB) is a worldwide burden whose total control and eradication remains a challenge due to factors including false positive/negative diagnoses associated with the poor sensitivity of the current diagnostics in immune-compromised and post-vaccinated individuals. As these factors complicate both diagnosis and treatment, the early diagnosis of TB is of pivotal importance towards reaching the universal vision of a TB-free world. Here, an aptasensor for signaling an interferon gamma (IFN-γ) TB biomarker at low levels is reported. The aptasensor was assembled through gold-thiol interactions between poly(3,4-propylenedioxythiophene), gold nanoparticles, and a thiol-modified DNA aptamer specific to IFN-γ. The aptasensor sensitively detected IFN-γ in spiked pleural fluid samples with a detection limit of 0.09 pg/mL within a linear range from 0.2 pg/mL to 1.2 pg/mL. The good performance of the reported aptasensor indicates that it holds the potential for application in the early diagnosis of, in addition to TB, various diseases associated with IFN-γ release in clinical samples.

Keywords: interferon gamma; phase angle; pleural fluid; poly(3,4-propylenedioxythiophene) nanocomposite; tuberculosis diagnosis.

Figure 1

EIS Nyquist (A) and bode plots (B,C) of (a) the PProDOT, (b) PProDOT–AuNPs, (c) PProDOT–AuNPs-Aptamer, and (d) PProDOT–AuNPs–Aptamer–MCH (aptasensor) in the frequency range from 0.1 Hz to 100 kHz with 10 mV amplitude in PBS, pH 7.4. (D) The Randles equivalent circuit was used to fit experimental data.

Figure 2

Phase angle signal in the absence (0 pg/mL) and presence (2 pg/mL) of IFN-γ upon incubation in phosphate buffer (left axis) and pleural fluid (right axis). The higher signal change in PLF is associated with the complexity of PLF.

Figure 3

(A) Aptasensor responses of IFN-γ ranging from 0.2 pg/mL to 2.2 pg/mL in spiked PLF between 0.1 Hz and 100 kHz at an amplitude of 10 mV. (B) The calibration curve for the aptasensor during the detection of IFN-γ in comparison to the control sensor fabricated without a recognition element. (C). Linear curve drawn from the linear regression of (A), from which a detection limit of 0.09 pg/mL was determined. The error bars represent the averages of three experimental results.

Scheme 1

Illustration of the aptasensor fabrication strategy based on the gold–thiol interactions between the PProDOT, AuNPs, and the thiol-modified anti-IFN-γ aptamer. To avoid non-specific adsorption between the analyte, 6-mercapto-1-hexanol (MCH) backfills the free PProDOT–AuNP film. When introduced, IFN-γ forms a complex with the aptamer.