Low-Cost Nucleic-Acid-Based Radial Flow Assay for the Detection of GSTP1 Promoter DNA Methylation in Prostate Cancer

DNA methylation of the glutathione S-transferase pi 1 (GSTP1) promoter is a widely studied epigenetic biomarker for prostate cancer; however, its direct detection in genomic DNA remains analytically challenging without complex chemical or amplification-based workflows. Here, we report a nucleic acid-based radial flow assay (NABRFA) that enables visual and pattern-based detection of gene-specific DNA methylation using gold nanoparticle (AuNP)-conjugated oligonucleotide probes. Thiol-modified single-stranded DNA probes targeting the GSTP1 CpG island (5'ThG) were conjugated to AuNPs to form stable probe-nanoparticle constructs that retain colloidal stability under high ionic strength conditions (0.5 M NaCl). Upon hybridization with methylation-protected GSTP1 DNA, the resulting AuNP-DNA complexes exhibit hybridization-dependent modulation of transport and retention on a porous nylon membrane, generating characteristic concentric radial patterns. These patterns arise from spatial separation between retained hybridized complexes and outwardly transported unbound probe-functionalized nanoparticles, enabling direct visual discrimination of target presence. The assay demonstrated concentration-dependent pattern evolution, with visual detection achievable down to 1 ng of target DNA and an analytically determined limit of detection of approximately 32 ng, based on image-derived gray value analysis. The human prostate cancer cell line LNCaP, known for GSTP1 promoter hypermethylation, was used as the test model for assay validation. Comparative analysis using methyl-sensitive restriction enzyme-treated native genomic DNA from the human osteosarcoma MG-63 cell line (non-prostate cancer, GSTP1 methylation-negative control) and the human lung fibroblast WI-38 cell line (non-cancerous, GSTP1 methylation-negative control) confirmed assay specificity. By coupling sequence-specific hybridization with transport-mediated nanoparticle pattern formation, NABRFA provides a label-free and conversion-free analytical strategy for detection of methylation-protected GSTP1 DNA using minimal instrumentation. This work establishes a proof-of-concept membrane-based, transport-driven sensing approach for epigenetic biomarker detection and highlights its potential for integration into simplified molecular diagnostic workflows.