Onsite DADQs-assisted chemiluminescence wavelength shift from luminol µPADs to tetracyanoquinodimethane-based fluorophores enabling sensitised emission of AuNPs in point-of-source testing (PoST) multimode device.

The rapid advancement of small-molecule-based fluorophores is attributed to their highly tunable optical properties, which enable notable applications in biomedical, environmental research and demand cost-effective, user-friendly alternatives for deployment in remote locations. Accordingly, we have synthesised and characterised a new class of simple tetracyanoquinodimethane (TCNQ) derivatives with different amine substituents referred to as diaminodicyanoquinodimethane fluorophores (DADQs), i.e. BMOPDQ [1], BCDMDQ [2], BEPDQ [3], BMPPDQ [4], and BCPPDQ [5]. At the outset, herein we introduce and demonstrate a novel approach that utilises a sequential sensitised emission process, in which the first step involves DADQ-assisted chemiluminescence (CL) wavelength shift, followed by optical sensitisation of gold nanoparticles (AuNPs), in a point-of-source testing (PoST) multimode optical detection system. The photons emitted from the luminol-based chemiexcited species are transferred to DADQs via an optical absorption. The resulting green emission from DADQs ascertains the sensitised emission of AuNPs, which emit a red signal. Moreover, the blue emission of the chemiluminiscent signal can be shifted to longer wavelengths without any complex instrumental setup, making it suitable for real-world applications. Thus, the PoST platform provides a compact, sensitive, and selective method for detecting various analytes, including biomarkers and metal ions, using small sample volumes without the requirement of bulky instrumentation. Furthermore, a PoST-reliable device could enable luminescence techniques to reach remote areas for portable on-site testing.