Multi-technique characterization of gold nanoparticle-based DNA biosensor with smartphone-enabled photometry for accelerated detection of Campylobacter jejuni

Campylobacter is one of the most infectious foodborne pathogens, often associated with consuming contaminated poultry products. Many Campylobacter infections are not reported until the symptoms become severe, making it necessary to detect them rapidly in food production systems as part of a preventative intervention strategy. In this study, a gold nanoparticle (GNP)-based DNA biosensor that utilizes digital photometric signals from smartphone images was developed to rapidly detect Campylobacter jejuni in drainage water and poultry rinse samples. Spectrophotometric measurements, hydrodynamic size, zeta potential, and dark-field microscopy confirm that hybrids were successfully formed between GNP, oligonucleotide probe, and C. jejuni DNA using an in-situ approach. Triggering GNP aggregation upon hybridization, the nano-biosensor signals obtained through smartphone-enabled digital photometry were strongly correlated with spectrophotometry. Based on the smartphone-enabled signal, the nano-biosensor demonstrated a high degree of selectivity for C. jejuni and detected 103 and 106 colony-forming units (CFU)/mL in unenriched drainage water and poultry rinse samples, respectively. This work demonstrates a GNP-based DNA biosensor employing cadF-targeted hybridization and smartphone-enabled digital photometry for the detection of Campylobacter jejuni in real samples. Diffusion-limited aggregation of unhybridized GNPs yields distinct optical responses, enabling the detection of target DNA in drainage water and poultry rinse. These findings provide a foundation for future validation studies in samples critical to monitoring foodborne pathogens across various food production and processing systems. Moreover, they highlight the potential of the smartphone-aided nano-biosensing system as a cost-effective, field-deployable means of pathogen surveillance.