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Electrochemical sensors, enhanced by nanomaterials (NMs) like carbon nanofibers and metal nanoparticles, are crucial for detecting heavy metals in water and food. Sensor performance depends on factors such as sensitivity, detection limit, and stability, improved through surface modifications (drop casting, SAMs, etc.). Nano-enzyme catalytic activity is influenced by external (pH, electrolyte) and intrinsic (size, shape) factors. Signal transduction at the nanoscale interface is vital for sensor efficacy. Rapid electrochemical and colorimetric nanosensors enable real-time, on-site detection, improving accessibility. Heavy metal contamination poses serious health risks due to bioaccumulation, necessitating accurate detection. Electrochemical sensors offer low detection limits and versatile signal reporting. Diverse analytical techniques (potential analysis, conductometry, colorimetry) provide rapid, sensitive, and cost-effective detection. Waste-derived carbon nanodots (CNDs) offer a sustainable approach for heavy metal detection, combining fluorometric and electrochemical capabilities. Novel zeolite-clay composite membranes, made from inexpensive materials, show promise for heavy metal removal, with electrochemical investigations optimizing their performance. Porous organic frameworks (POFs) further enhance sensor sensitivity, selectivity, and stability, enabling the development of portable and cost-effective devices for environmental monitoring.

electrochemistry, greatly enhancing the sensor’s vulnerability, selectivity,
and steadiness. This technique encompasses carbon materials
[41] nanofibers, threads, fullerenes, graphene, and graphitic substances,
offering diverse functionalities for sensor development [21]. Current
developments in the fabrication of cutting-edge NMs include metal
nanoparticles, metal oxide NMs, carbon NMs polymers, and biomaterials
as the basis for electrochemical sensor platforms [42]. Moreover,
Nano-NaOH was prepared via the electrodeposition method as a novel
sensing NM [43]. Therefore, the use of printed electrodes and their
modifications are explored in detail in this review.
The convergence of nanotechnology and printing unlocks a fertile
ground for exploring novel printed electrode materials. The performance
of electrochemical sensors hinges on critical properties like
sensitivity, detection limit, dynamic range, selectivity, linearity,
response time, and stability, specifically exploring various techniques to
modify the electrode surface. These techniques include drop casting,
self-assembled monolayers (SAMs), electro-polymerization, and molecularly
imprinted polymers (MIPs) [21,44]. This is particularly true for
sensors utilizing nano-electrodes, which have become a hotbed of
research. Scientists are actively pinpointing and fine-tuning these parameters
to optimize the performance of next-generation electrochemicals
and biosensors. As evidenced by studies on biocatalytic metal
nanoparticle-based sensors [45,46] research in this area holds immense
promise.
The investigation reveals that both external factors such as pH and
the kind and chemical composition of the electrolyte and intrinsic
characteristics of nano enzymes such as composition, size, and shape
have a noteworthy influence on the catalytic activity of these molecules.
Studies confirm the importance of signal transduction in electrochemical
sensors. Notably, the nanoscale structures at the interface between
the sensing element and the biological sample play a critical role
in determining the overall sensor efficacy [20]. The most popular
methods of surface modification, electrochemical transduction pathways
and selection of the recognition receptor molecules affect the
sensor’s final sensitivity [30]. In addition, the development of rapid
electrochemical and colorimetric nano-sensors empowers real-time,
on-site detection of HMIs. This advancement allows for visual,
point-of-use, and in-field analysis, significantly improving accessibility
and monitoring capabilities [47].
There is a justifiable concern on the presence of heavy metals in the
environment as they are more difficult to decontaminate than organic
contaminants and tend to accumulate in living things. Because of their
sluggish removal rates, this bioaccumulation presents a serious risk to
health, with the potential to cause developmental issues and even organ
failure. The accurate and precise detection of toxic metal ion concentrations
in drinkable water and food samples is an essential requirement
for ensuring human health and safety [48,49]. Safeguarding our water
supplies demands real-time, high-resolution measurement techniques to
pinpoint ultra-low levels of heavy metals like U, Pb, Cd, Cr, and As in
water and food. In recent decades, electrochemical detection through
sensors has transformed water pollutant monitoring by converting
chemical changes into measurable electrical signals. Two of the most
widely used characteristics of an electrochemical sensor for multiple
applications are its low theoretical detection limits, which stem from the
variations in Faradaic and non-Faradaic currents, and its variability in
reporting signals, such as voltage, current, overall power output, or
electrochemical impedance [50]. Generally, electrochemical sensors
possess immeasurable significance in analytical chemistry.
Diverse analytical techniques, such as potential analysis, conductometric,
and colorimetric offer distinct advantages, including rapid
response times, high miniaturization potential, high sensitivity, and
selectivity, cost-effectiveness, and operational simplicity, making them
ideal candidates for this critical application [50,51]. Modifiers, coating
materials, and electrode type possess a significant impact on the selectivity
and efficiency of electrochemical sensors [52]. Waste-derived
Carbon Nanodots (CNDs) have emerged as a promising tool for water
Talanta Open 10 (2024) 100354
quality monitoring. By transforming beer industry waste into CNDs
[53], researchers have developed a sustainable and efficient method for
detecting multiple heavy metals simultaneously. These CND-based
sensors offer both fluorometric and electrochemical detection capabilities,
enabling rapid and accurate analysis of water samples. This
approach not only addresses environmental pollution but also promotes
circular economy principles by repurposing waste materials.
A new type of membrane called zeolite-clay composite is being
developed as a practical heavy metal removal method [54]. Natural clay
and diatomite are two inexpensive, abundant elements used for making
this novel substance. These elements are mixed precisely to produce a
membrane with remarkable water-purification capabilities. Important
insights into the surface properties of the membrane are obtained by
electrochemical investigations, which allow for optimization for heavy
metal absorption. The development of sustainable and effective water
treatment technologies that tackle the urgent problem of heavy metal
contamination is greatly promising from the current study. Recent
progress in porous organic frameworks (POFs) has opened new avenues
for electrochemical sensing of environmental pollutants [55]. The
exceptional porosity, large surface area, and tunable functional groups
of POFs make them ideal platforms for capturing and detecting a wide
range of contaminants. Researchers have successfully incorporated POFs
into electrochemical sensors to enhance sensitivity, selectivity, and
stability. These advanced materials show great promise for developing
portable and cost-effective devices for monitoring water and air quality,
contributing to early warning systems and effective pollution control
strategies. Hence, the electrochemical sensing of the selected metals
discussed in subsequent subsections with a focus on these methods.