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Background: Currently, the environmental and biological samples, such as water, soil, vegetables, etc., are highly contaminated with metal ions, anions and pesticides. For analysis of these toxic substances from the environmental and biological samples, sophisticated and expensive instruments are being used. The present work deals with the development of a simple, faster, sensitive and economical method for the analysis of toxic substances present in different samples. Methods: The general methods for synthesis and characterization of metallic (Ag, Au, Cu and graphene) nanoparticles and conductive polymer for the development of conductive nano-ink and fabrication of paper substrate by direct deposition and laser, wax, or inkjet printing techniques, have been reported. Results: Paper-based sensors fabricated with different nanomaterials used as colorimetric, electrochemical and fluorescence-based chemical sensors for the quantitative determination of pesticides and toxic metal ions in various biological and clinical samples have been comprehensively discussed in this review. Conclusion: The low-cost, rapid, eco-friendly, flexible, portable, and paper-based sensors using nanoparticles (NPs) are in demand for on-site detection of different chemical constituents present in various environmental, biological and clinical samples.

The paper-based sensing devices have drawn a broad interest in analytical chemistry for colorimetric and fluorescent-based analysis of biological, environmental, clinical, and food samples. It is due to the simple, rapid, biodegradable, user-friendly, less expensive, and low waste generation into the environment. Here, the recent development of paper-based sensors fabricated with different noble metal nanoparticles (NPs) and semiconductor and carbon quantum dots (QDs) is demonstrated to analyze several chemical substances from various samples. User-friendly and portable recording devices such as digital cameras, smartphones, scanners, etc. along with color detecting softwares are employed to measure the color intensity of nanomaterials fabricated paper devices after the deposition of a sample solution containing various chemical substances. The advantages and disadvantages of incorporating nanomaterials in the paper substrate (direct deposition, inkjet printing, screen printing and wax printing) are illustrated. The mechanism for colorimetric, fluorescence, phosphorescence, and chemiluminescence sensing using noble metal NPs (Ag, Cu, and Au), semiconductors, and carbon QDs for the determination of metal ions, anions, pesticides, biomolecules, and other toxic chemical substances are discussed. Thus, this review article would be highly useful for scientists and researchers to design colorimetric sensors to monitor chemical toxicants in clinical, environment, foods, and many other related samples.