Toward point-of-care cancer diagnostics: gold nanoparticle-based colorimetric sensors

Nowadays, cancer has become one of the major causes of mortality all over the world, irrespective of age and gender. The early detection of cancer can markedly enhance patient survival outcomes. Cancer cells are analyzed by comparing the optimum concentration of different types of biomarkers, including alpha-fetoprotein (AFP), prostate-specific antigen (PSA), microRNA-21, and carcinoembryonic antigen (CEA), in biological samples. These biomarkers play a crucial role in the early detection, screening and treatment of cancer. Novel colorimetric assays based on modified AuNPs are discussed in this review, which have opened a new avenue for the facile, point-of-care diagnosis of cancer. Due to their unique characteristics such as surface plasmon resonance (SPR), AuNPs provide a selective, trustworthy and simple strategy to detect cancerous cells by visualizing a color change when used in colorimetry. The principles of the sensing methods (aggregation, anti-aggregation, etching, and enzyme-mimetic activity) are illustrated in this review. Besides, some portable devices, such as paper-based devices (PADs), barcodes, and lateral flow assays (LFTs), are mentioned, which have made this complicated detection process as convenient as a pregnancy strip test. However, these devices are primarily limited by their low sensitivity and inadequate capability for accurate quantitative analysis. This review highlights the progress of paper-based colorimetric sensing devices for the detection of cancers, such as breast cancer, prostate cancer, pancreatic cancer, and bladder cancer. Furthermore, we outline the key advantages of these devices and emphasize their major limitations. Finally, we have also mentioned some perspectives that may improve the sensitivity of these colorimetric devices as biosensors.