Ultrasensitive photoelectrochemical immunosensor based on floral cluster SnS2/ZnCdS heterostructure for the detection of CA199

Abstract

The early and accurate detection of tumor markers is crucial for cancer diagnosis, prognosis, and treatment monitoring. Carbohydrate antigen 199 (CA199), as a key biomarker of pancreatic, gastric, and colorectal cancers, is widely used in the clinical management. The development of sensitive, rapid and cost-effective detection methods for CA199 is of paramount importance in improving early detection rates and patient outcomes. In this study, we present a novel photoelectrochemical (PEC) immunosensor based on a SnS₂/ZnCdS heterostructure designed for the ultrasensitive detection of CA199. The unique heterojunction between SnS₂ and ZnCdS enhances photocurrent generation by effectively suppressing charge recombination and improving charge separation. Furthermore, the flower-like morphology of the heterostructure further boosts light absorption and photogenerated carrier transport, resulting in significantly enhanced sensor performance. This label-free PEC immunosensor exhibits outstanding stability, reproducibility and selectivity, with a broad detection range from 0.01 to 1000 U/mL and an ultra-low detection limit of 1.00 × 10^-3 U/mL. These features demonstrate the potential of this sensor as a powerful tool for sensitive CA199 detection, offering promising applications in cancer diagnostics and monitoring.

Keywords: CA199; SnS2/ZnCdS; flower-like morphology; heterojunction; photoelectrochemical immunosensor.

FIGURE 1

Construction process of PEC immunosensor for CA199 detection.

FIGURE 2

TEM and XRD characterization of SnS₂, ZnCdS and SnS₂/ZnCdS. (A) SEM image of SnS₂; (B) SEM images of ZnCdS; (C) SEM images of SnS₂/ZnCdS; (D) XRD spectra of SnS₂; (E) XRD spectra of ZnCdS; (F) XRD spectra of SnS₂/ZnCdS.

FIGURE 3

SnS₂/ZnCdS element mapping and HRTEM mapping. (A) Elemental mapping of SnS₂/ZnCdS; (B–E) mapping images of S, Cd, Sn and Zn; (F) HRTEM images of SnS₂/ZnCdS.

FIGURE 4

Photoelectric chemical characterization of PEC immunosensor. (A) The electron transfer mechanism in PEC immunosensors without antigens/antibodies; (B) The photocurrent response curve of the photoactive material and (C) EIS Nyquist plots of (a) ITO, (b) ITO/SnS₂/ZnCdS,(c) ITO/SnS₂, and (d) ITO/ZnCdS. (D) The electron transfer mechanism in PEC immunosensors with antigen-antibody complexes; (E) Photocurrent response curve and (F) EIS Nyquist plots of (a) ITO, (b) ITO/SnS₂/ZnCdS, (c) ITO/SnS₂/ZnCdS/TGA, (d) ITO/SnS₂/ZnCdS/TGA/EDC/NHS, (e) ITO/SnS₂/ZnCdS/TGA/EDC/NHS/anti-CA199, (f) ITO/SnS₂/ZnCdS/TGA/EDC/NHS/anti-CA199/BSA, (g) ITO/SnS₂/ZnCdS/TGA/EDC/NHS/anti-CA199/BSA/CA199.

FIGURE 5

Optimization of experimental conditions. (A) Concentration of SnS₂, (B) Concentration of ZnCdS, (C) Concentration of AA, (D) PH of PBS. All data reported are presented as the mean ± SD (n = 3).

FIGURE 6

Photocurrent response curves and standard curves of CA199. (A) Photocurrent response curves of CA199 (from a to f: 0.01 U/mL, 0.1 U/mL, 1 U/mL, 10 U/mL, 100 U/mL and 1000 U/mL), (B) Standard curves of PEC immunoassay.

FIGURE 7

Stability, reproducibility, and selectivity of PEC immunosensor. (A) Stability assessment of the PEC immunosensor under on/off irradiation cycles (CA199 concentration 1 U/mL). The applied potential is 0 V), (B) Stability assessment of PEC immunosensors at different time periods, (C) Repeatability analysis of five groups of sensors constructed simultaneously, (D) Selective analysis of CA199 PEC immunosensors. The distractors added by each sensor are as follows: (1) blank samples, (2) 100 ng/mL CEA, (3) 100 ng/mL NSE, (4) 100 ng/mL CTnI, (5) 1 U/mL CA199, (6) 1 U/mL CA199 + 100 ng/mL CEA, (7) 1 U/mL CA199 + 100 ng/mL NSE, (8) 1 U/mL CA199 + 100 ng/mL CTnI.