Green Synthesis of Carbon Quantum Dots Derived from Orange Peel for High-Sensitivity pH Biosensing

Ayush Tawade; Ashwini Thakre; C. Ravikumar; Diwakar Shende; Kailas Wasewar

doi:10.33927/hjic-2025-23

Authors

Ayush Tawade MIT School of Bioengineering Sciences and Research, MIT ADT University, Loni Kalbhor, Pune, Maharashtra 412201, INDIA
Ashwini Thakre Department of Chemical Engineering, Visvesvaraya National Institute of Technology (VNIT), South Ambazari Road, Nagpur, Maharashtra 440010, INDIA
C. Ravikumar Department of Chemical Engineering, Indian Institute of Technology (IIT) Dharwad, Chikkamalli-gawad, Dharwad, Karnataka 580011, INDIA
Diwakar Shende Department of Chemical Engineering, Visvesvaraya National Institute of Technology (VNIT), South Ambazari Road, Nagpur, Maharashtra 440010, INDIA
Kailas Wasewar Department of Chemical Engineering, Visvesvaraya National Institute of Technology (VNIT), South Ambazari Road, Nagpur, Maharashtra 440010, INDIA

DOI:

https://doi.org/10.33927/hjic-2025-23

Keywords:

carbon quantum dots, orange peel, green synthesis, pH biosensor, microwave-assisted synthesis

Abstract

Carbon quantum dots (CQDs) are nanoscale, fluorescent carbon-based substances known for their outstanding biocompatibility, solubility in water and flexible optical characteristics. The environmentally-friendly creation of such nanoparticles through the use of non-toxic, renewable resources and energy-efficient techniques is known as green synthesis. Utilizing orange peel as an affordable, sustainable precursor, the ecologically-friendly synthesis of CQDs and nitrogen-doped CQDs (NCQDs) using both hydrothermal and microwave-assisted methods are presented. Small, homogeneous CQDs (2–3 nm) with a modest quantum yield (~11%) were created by the hydrothermal method, but the microwave-assisted method instantly produced larger CQDs (4–8 nm) with improved fluorescence intensity and enhanced quantum yield (~54%). The optical properties of both CQDs and NCQDs at different pH levels (4, 7 and 10) were studied using UV-Vis spectroscopy. With a significant redshift in absorbance peak wavelengths from 429 nm at pH 4 to 445 nm at pH 10, CQDs exhibited robust pH-responsive activity and high pH sensitivity. The slightly blue-shifted but more stable optical response with NCQDs, on the other hand, makes them suitable for applications requiring signal reliability. A pH biosensor is an analytical tool used in biomedical, industrial and environmental monitoring to analyze changes in hydrogen ion concentration, providing a rapid, visual or digital input about the acidity or alkalinity of a given environment. These findings demonstrate that CQDs and NCQDs generated from orange peel are viable, non-toxic and promising nanomaterials for colorimetric pH biosensing. Each has unique advantages tailored to particular sensing conditions that can be applied to intracellular pH imaging, water and soil quality evaluation, smart packaging, food freshness detection, biological diagnostics (such as wound and saliva monitoring) as well as medicine stability tracking.