Cellphone-Aided Attomolar Zinc Ion Detection Using Silkworm Protein-Based Nanointerface Engineering in a Plasmon-Coupled Dequenched Emission Platform
Aayush Rai, Seemesh Bhaskar, Narendra Reddy, Sai Sathish Ramamurthy
Abstract
Sustainable chemistry principles involve go-green approaches for the synthesis of nanomaterials. Recent interest has been toward the use of renewable raw materials as precursors for the reduction of metal ions to nanoparticles (NPs). However, utility of residues and byproducts for plasmonic applications that could potentially add an immense value in interfacial applications is rarely attempted. Here, the silkworm pupae that contain up to 40% proteins and are generally discarded as a byproduct after reeling the silk fibers were collected, and the proteins in them were extracted. The protein hence obtained is termed silkworm protein (SWP). A simple mixture of metal ions (Ag+ and Au3+) with SWP and exposure to UV irradiation at defined intervals of time presented unique nanogeometries for plasmonic applications. The frugal bioinspired nanoengineering protocol developed here paved the way for monometallic (AgNPs and AuNPs) and heterometallic (AgAu) nanohybrids with remarkable optical and morphological properties. The obtained sharp-edged NPs with intense transverse and longitudinal localized surface plasmon resonances were studied on metallic thin films sustaining propagating surface plasmon polaritons to generate amplified and integrated hotspots. This was utilized for realizing tunable, highly directional, p-polarized, and augmented surface plasmon-coupled emission using a mobile phone-based detector. The unaccustomed 1300-fold enhancement of dequenched fluorescence achieved for the first time was employed for attomolar mobile phone-based sensing of environmentally and biologically relevant zinc ions with excellent correlation in comparison with conventional and cost-intensive detectors. This frugal bio-nanoinspired technology is amenable for resource-scarce settings and enhances adoption at the bottom of the pyramid for point-of-care applications. We strongly believe that the disruptive engineering developed in this study would open new doors for exploring and utilizing waste byproducts from several other industries including sugar, paper, electronics, and aquaculture for high-end photonic biosensor development.