An Ultrasensitive Norfentanyl Sensor Based on a Carbon Nanotube-Based Field-Effect Transistor for the Detection of Fentanyl Exposure

Abstract

The opioid crisis is a worldwide public health crisis that has affected millions of people. In recent years, synthetic opioids, primarily illicit fentanyl, have become the primary driver of overdose deaths. There is a great need for a highly sensitive, portable, and inexpensive analytical tool that can quickly indicate the presence and relative threat of fentanyl. In this work, we develop a semiconductor enriched (sc-) single-walled carbon nanotube (SWCNT)-based field-effect transistor (FET) biosensor functionalized with norfentanyl antibodies for the sensitive detection of norfentanyl, the primary inactive metabolite of fentanyl, in urine samples. Different sensor configurations were explored in order to obtain the most optimized sensing results. Moreover, by employing the "reduced" antibody, we achieved orientated immobilization of the norfentanyl antibody and thus brought the antigen-antibody interaction closer to the sensor surface, further improving the sensitivity. The reported norfentanyl biosensors have a limit of detection in the fg/mL region in both calibration samples and synthetic urine samples, showing ultrasensitivity and high reliability.

Keywords: biosensor; carbon nanotube; fentanyl overdose; field-effect transistor; norfentanyl; opioid.

Figure 1

Norfentanyl antibody functionalized SWCNT-based FET biosensor. (a) Top: Optical image of the sensing chip with 8 devices. Bottom: The sensing chip was wire-bonded in a package for measurements. (b) Schematic illustration of a norfentanyl antibody functionalized SWCNT-based FET biosensor via direct coupling approach. (S: Source; D: Drain.) (c) FET transfer characteristics of each functionalization step using a direct coupling approach. (d) Schematic illustration of a norfentanyl antibody functionalized SWCNT-based FET biosensor via the AuNP approach. (e) FET transfer characteristics of each functionalization step using the AuNP approach.

Figure 2

Device characterizations. (a) SEM image and AFM image (inset) of SWCNT networks deposited between source and drain electrodes on a FET device. (Inset scale bar: 500 nm) (b) SEM image and AFM image (inset) of SWCNT networks after norfentanyl antibody functionalization. (Inset scale bar: 500 nm) (c) D and G peak regions of Raman spectra of the SWCNTs before and after the immobilization of norfentanyl antibody. The Raman spectra were recorded using a 638 nm excitation laser. All spectra were normalized to the G peak at 1587 cm^–1. (d) Radial breathing mode (RBM) regions of Raman spectra were recorded using a 785 nm excitation laser. All spectra were normalized to the Si peak at 507 cm^–1 (not shown). (e) SEM image and AFM image (inset) of Au-sc-SWCNTs and (f) norfentanyl ab-Au-sc-SWCNTs (inset scale bar: 500 nm). (g) Raman spectra of the FET device during each functionalization step using the AuNP approach. The Raman spectra were recorded using a 638 nm excitation laser. All spectra were normalized to the Si peak at 507 cm^–1 (denoted by the asterisk).

Figure 3

Norfentanyl sensing in PBS. (a) Norfentanyl sensing performance using ab-sc-SWCNT devices (direct coupling approach). Inset shows FET transfer characteristics of norfentanyl ab-sc-SWCNT devices upon adding increasing concentrations of norfentanyl. (b) Norfentanyl sensing performance using norfentanyl ab-Au-sc-SWCNT devices (AuNP approach). Inset shows FET transfer characteristics of norfentanyl ab-Au-sc-SWCNT devices upon adding increasing concentrations of norfentanyl. (c) Control experiments with nonspecific drug metabolites using norfentanyl ab-Au-sc-SWCNT devices.

Figure 4

Norfentanyl sensing in synthetic urine. Direct coupling approach: (a) FET characteristic curves for norfentanyl sensing in 1000× diluted synthetic urine using norfentanyl ab-sc-SWCNT devices; (b) Calibration plot of the devices for norfentanyl sensing in different dilutions of synthetic urine. AuNP approach: (c) FET characteristic curves for norfentanyl sensing in synthetic urine without dilution using norfentanyl ab-Au-sc-SWCNT devices; (d) calibration plot of the devices for norfentanyl sensing in different dilutions of synthetic urine. All data points plotted in the calibration plots are the mean ± standard error (SE). The number of devices (n) used for calculation are indicated in the parentheses in the legend.

Figure 5

Norfentanyl sensing using reduced norfentanyl antibody-functionalized sc-SWCNT FET biosensors. (a) Binding of whole and reduced IgG antibodies on AuNPs. (b) Norfentanyl sensing in PBS and synthetic urine using reduced norfentanyl ab-Au-sc-SWCNT devices.

Figure 6

Norfentanyl sensing with flexible gold FETs with a coplanar gate. (a) Optical image of a flexible gold FET with a coplanar gate (AUFET). The zoom-in view is an illustration of interdigitated electrodes. (b) Norfentanyl sensing using AUFET by functionalizing the sc-SWCNTs with norfentanyl antibody via the direct coupling approach. (c) Norfentanyl sensing using AUFET by attaching the norfentanyl antibodies on the Au gate (norfentanyl ab@Au gate). (d) Norfentanyl sensing in synthetic urine using norfetanyl ab@Au gate AUFET. (e) Comparison of norfentanyl sensing performances between whole antibody and reduced antibody functionalized AUFET.