Nickel detection advances environmental and biological health monitoring systems.

The increasing prevalence of nickel in both industrial processes and biological systems necessitates sensitive and reliable detection methods, as excessive exposure can pose significant health risks. Researchers are now focusing on the potential of nanoscale materials to address this challenge, leveraging their unique optical properties for accurate sensing. Sudhanshu Naithania, Heenaa, and colleagues, from the University of Petroleum and Energy Studies alongside Franck Thetiot from the Centre National de la Recherche Scientifique, present a comprehensive review entitled ‘Nanoparticles and Quantum Dots as Emerging Optical Sensing Platforms for Detection: Recent Approaches and Perspectives’. The study examines recent advances in the design of optical nanosensors, specifically utilising metal nanoparticles, quantum dots and carbon dots, to selectively detect nickel ions in environmental and biological samples, whilst also comparing performance characteristics and outlining future research directions.

Nickel’s widespread presence necessitates careful monitoring due to potential environmental and health impacts, as this ubiquitous metal plays a critical role across ecological, industrial, and biological systems. While essential for numerous biological processes in organisms ranging from plants to archaea, excessive or deficient levels of nickel ions pose significant health risks to both humans and the environment, prompting regulatory bodies like the World Health Organization to establish stringent concentration limits in drinking water, currently set at 0.02 mg/L. Consequently, the development of effective and selective detection methods for nickel ions remains crucial for applications in environmental monitoring and biological studies, driving research towards innovative sensing technologies.

Conventional analytical techniques, such as voltammetry and various spectroscopic methods including inductively coupled plasma mass spectrometry (ICP-MS), provide precise quantification of nickel concentrations, yet these methods typically require laboratory infrastructure and lack adaptability for on-site or field-based measurements. This limitation hinders real-time monitoring and rapid assessment of nickel contamination in remote or challenging environments, prompting a focus on developing more accessible and versatile detection strategies. Optical sensors, employing colorimetric or fluorogenic principles, represent a rapidly evolving field for nickel detection, offering a potentially simpler and more portable alternative to traditional methods.

Nanomaterials, including metal nanoparticles, quantum dots, and carbon dots, are increasingly incorporated into these sensors to enhance their sensitivity and selectivity, providing unique optical properties that can be tailored to specifically bind nickel ions and improve detection accuracy. Metal nanoparticles exhibit surface plasmon resonance, a phenomenon where collective oscillations of electrons are excited by light, resulting in a characteristic colour change upon nickel ion binding. Quantum dots, semiconductor nanocrystals, emit light at specific wavelengths dependent on their size and composition, with nickel ion presence quenching this fluorescence or shifting the emission wavelength. Carbon dots similarly exhibit fluorescence modulated by target ion binding.

Unlike traditional sensors, these nanosensors leverage the unique optical properties of materials to achieve enhanced sensitivity and selectivity, employing design strategies to functionalise these nanomaterials with specific receptors that selectively bind to nickel ions. This functionalisation often involves organic ligands, polymers, or biomolecules, carefully chosen for their affinity towards the target ion and their ability to induce a measurable optical signal upon binding.

A significant methodological challenge lies in achieving both high sensitivity and selectivity simultaneously, as many nanomaterials exhibit inherent fluorescence or absorb light across a broad spectrum, leading to background noise and false positives. To overcome this, researchers are exploring strategies to enhance the signal-to-noise ratio, such as core-shell structures where a highly fluorescent core is coated with a selective layer, or employing signal amplification techniques like surface-enhanced Raman scattering. Furthermore, the stability and biocompatibility of the nanosensors are critical considerations, particularly for applications in biological sensing, prompting investigations into encapsulating the nanomaterials in protective coatings or modifying their surfaces with biocompatible polymers to prevent aggregation, degradation, and toxicity.

Comparing the performance of different nanosensors requires careful consideration of several key parameters, including detection limit, selectivity, response time, and operational stability. The detection limit, representing the lowest detectable nickel ion concentration, serves as a crucial metric for assessing sensitivity. Selectivity, the ability to distinguish nickel ions from other interfering species, is equally important for accurate measurements in complex matrices, while response time and operational stability determine the speed and longevity of analysis. Future research directions include the development of multiplexed sensors capable of simultaneously detecting multiple ions, and the integration of nanosensors with microfluidic devices for automated and high-throughput analysis.

Recent advances in nanomaterial-based optical sensors significantly benefit nickel detection, and the increasing prevalence of nickel in industrial processes, healthcare, and everyday life necessitates accurate and sensitive detection methods, particularly concerning potential health risks associated with excessive exposure. These materials offer enhanced sensitivity and selectivity compared to traditional sensors, and researchers actively explore diverse design strategies to optimise nanosensor performance, focusing on selective detection of nickel ions in both environmental and biological samples.

Performance comparisons between different nanosensor designs reveal a complex interplay between material properties, surface functionalisation, and detection limits. Factors such as nanoparticle size, shape, and composition significantly influence the sensor’s response to nickel ions, and surface modification with specific ligands or receptors further enhances selectivity, enabling discrimination of nickel from other interfering ions.

This work demonstrates a clear trend towards miniaturisation and integration of nanosensors into portable detection devices, promising real-time, on-site monitoring of nickel contamination in water sources, food products, and biological fluids. It underscores the potential of nanotechnology to contribute to environmental monitoring, public health, and industrial process control.

Currently, challenges remain in improving the long-term stability and reproducibility of these nanosensors, as many designs still suffer from issues such as nanomaterial aggregation, photobleaching, and susceptibility to environmental factors. Addressing these limitations requires further research into protective coatings, surface passivation techniques, and robust sensor architectures. Translating laboratory prototypes into commercially viable devices necessitates miniaturisation, integration with microfluidic systems, and development of user-friendly readout mechanisms. Future work should prioritise the development of multiplexed sensors capable of simultaneously detecting multiple metal ions, providing a more comprehensive assessment of environmental and biological samples.

Exploration of novel nanomaterials, such as two-dimensional materials and metal-organic frameworks, also holds promise for creating sensors with even greater sensitivity and selectivity. Ultimately, continued innovation in nanomaterial-based optical sensors will play a vital role in safeguarding environmental and public health. Accurate and reliable detection of nickel ions, alongside other heavy metals, is essential for monitoring pollution levels, assessing water quality, and ensuring the safety of food and pharmaceutical products, and the field stands poised for further advancements, driven by the ongoing pursuit of more sensitive, stable, and versatile sensing technologies.