Recent applications of hydrogels in food safety sensing

Access to safe food is essential
for human health.
Therefore, effective sensing of harmful substances in food is very necessary
.
Hydrogels with three-dimensional polymer network structure have the advantages
of good biocompatibility, large specific surface area, easy functionalization, flexible structure and good stability.
In recent years, stimulus-responsive hydrogels have attracted great attention
in the field of sensing for food safety monitoring.
To better understand the latest advances in real-time food safety monitoring of hydrogels, this review presents the latest applications
of hydrogel-based materials in the development of various food safety sensors.
Based on signaling patterns, these applications are compared, discussed, and summarized, the sensing mechanisms for each application are outlined, and the role of
hydrogels in each sensing strategy is highlighted.
Finally, the challenges and future trends
of hydrogel-based sensors are discussed.
Based on target-triggered optical, electrical, chemical, or biological signals, hydrogel-based materials exhibit superior performance
in food safety monitoring.
Although hydrogel-based materials show great potential, there is still a need for continuous efforts
before they can be widely used in commercial food safety control systems.
With the development of novel synthetic and functional methods, hydrogel-based sensors are expected to further promote the efficiency of
food safety sensing.
What's more, by combining with smart sensing devices, hydrogel-based sensors are expected to significantly improve the sensor's suitability
for real-world samples.

This review discusses the latest applications and roles
of hydrogels as sensing matrices in the determination of harmful substances in food.
Based on the optical, electrical, chemical, or biological signals of their target reaction, hydrogels can be used for target sensing
.
The inherent properties of hydrogels offer several advantages
for the construction of smart sensors.
On the one hand, their chemical diversity and the possibility of adjusting their properties favor the design of stimulus-responsive hydrogels, based on which the hydrogels themselves can be used to design sensors
.
On the other hand, the fabrication of various (bio)sensors is also possible
by loading smart molecular/nanomaterials into the highly wetted structure of hydrogels.
The non-rigid porous structure of hydrogels facilitates the immobilization of biomolecules and nanoparticles, which facilitates target recognition and signal amplification
.
The stable structure of the hydrogel prevents particle aggregation and signal changes
during detection.
Their porous structure allows the analyte of interest to penetrate through the hydrogel matrix while preventing the ingress
of large-sized food components.
In addition, they can extract analytes into hydrogel structures through solid-phase microextraction processes, and their shape adaptability makes them suitable for surface "paste-read" analysis
in real-world applications.
In recent years, there has been an increasing number of publications on sensors for hydrogels, and great efforts are being made
to realize the functionalization of hydrogels by introducing chemical molecules, biomolecules, and other smart nanomaterials.
Although hydrogel-based sensors have shown great potential, there are still some challenges that remain to be solved, providing plenty of room
for future research.

First, with the development of polymer engineering technology, it makes sense
to design and synthesize polymer networks through new crosslinking methods to achieve targeted regulation of functions, including selectivity, mechanical strength, conductivity and biological or chemical reaction properties of the target.
In addition, future developments based on hydrogel sensors will greatly benefit from increasingly precise control
of the structure and function of polymers as the basic building blocks of hydrogels.
Secondly, computational modeling and virtual simulation technology can be used to better explain the "composition-structure-performance" relationship of hydrogels and improve the structural design
of hydrogel sensors in the future.
Third, in addition to the specific sensor design, the combination of hydrogels with miniaturization technology can provide considerable application prospects
.
Integrating hydrogel-based sensors into chip-on-chip or microfluidic systems will facilitate the development of portable and miniaturized sensing tools
.
Finally, a hydrogel-based multi-target detection platform needs to be developed in a new generation of (bio)sensors to meet the need
for broad-spectrum detection of targets in one detection platform.

All in all, while hydrogel-based materials show great potential for rapid sensing for food safety, work needs to be done before they can be
widely used in commercial food safety control systems.
Through multidisciplinary collaborations such as polymer engineering, materials science, and biochemistry, hydrogel-based sensors are expected to further contribute to the efficiency of
food safety monitoring in the future.