Conventional biosensing methods are becoming outdated due to the complexity of biomolecules and the emergence of new pathogens. Their intricate detection and costly fabrication processes limit their application in biomedical research. Therefore, advanced sensing materials like photonic crystals (PCs) are needed for the timely identification, distribution, and decoding of various biomolecules.1
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PCs display distinctive structural colors due to their intrinsic band gap. Their organized structure, compact size, minimal analyte usage, high sensitivity, design flexibility, and integrability make them promising for biomedical research.2
PC-based materials are used in biomolecular screening, detection, real-time monitoring, and modification. With various fabrication methods yielding different properties, PCs have also expanded into therapeutic delivery systems.1
Principles and Properties of PCs
PCs consist of periodically arranged dielectric materials that manipulate and control light diffraction. These materials reflect specific light wavelengths according to the photonic band gap, producing unique structural colors. The inspiration for PCs comes from nature; for instance, opals and butterfly wings feature regular nanostructures and vibrant, distinct colors.1
The sensing process involves regulating the optical properties of PCs based on changes in film refractive index or lattice constant. Bragg’s law determines the photonic band gap, the design principle for PCs in biomedical applications.2 For example, if biomedicines are introduced to stimulate a PC system, the lattice constant and refractive index increase, causing a wavelength shift and color change.1
Applications of PCs in Biomedical Research
PC materials have gained significant attention in biomedical sciences due to their high sensitivity, selectivity, and continuous monitoring capabilities.1 PC-based biosensors simplify read-out methods through visibly detectable color changes.2 Additionally, the lower cost of bioassays promotes widespread application of these sensors in biochemistry and biomedicine.1
A notable application of PC biosensors is diabetes diagnosis. Glucose-sensitive inverse opal (IO) hydrogels incorporated into PCs change color when exposed to small amounts of glucose in bodily fluids like tears. Such sensitive glucose-detection materials can be integrated into contact lenses or ocular inserts, enhancing patient convenience and improving glycemic regulation.1
PCs also show great potential in drug delivery due to their biocompatibility and tunable optical properties, allowing them to carry multiple drug agents and deliver them controllably. IOs with three-dimensional periodic macro-porous structures and large surface areas demonstrate high drug delivery efficacy with minimal side effects.1
The easy-to-modify PC surfaces can be readily interfaced with various biomolecules. Choosing appropriate polymer matrices allows fabricated PCs to exhibit wavelength shifts in response to environmental stimuli. Thus, PCs can tune drug delivery and act as self-monitoring sensors.1
Timely tumor detection can reduce mortality rates. Tumor markers like alpha-fetoprotein (AFP) and carcinoembryonic antigen (CEA) are crucial for screening, diagnosing, and prognosis of malignant tumors. PC materials like silver nanoshell silica beads are used in multiple electro-chemiluminescent immunoassays for medical detection of CEA and AFP levels.1
The onset of multidrug resistance in tumor cells during chemotherapy often leads to treatment failure. PC-based multiplex detection of genes encoding proteins like multidrug resistance 1 (MDR1) and multidrug resistance-associated protein 1 (MRP1) facilitates rapid diagnosis.1
Challenges in PC Development
Compared to conventional methods, PC biosensors have commercialization potential. However, due to multiple challenges, applications like multiplex detection and gene screening are limited to laboratories.
Firstly, there is a lack of well-developed self-assembly methods for large-scale manufacturing of high-performance photonic structures. Transitioning from laboratory to commercial application and integration into existing biomedical workflows requires improvements in the resolution and discrimination abilities of PCs.1
Most biosensors can only perform single-shot measurements and cannot continuously observe a species, essential for many disease diagnoses. Additionally, the selectivity of PC sensors is limited, often impacted by the ionic strength of a solution or the presence of other analytes.1
The current PC design process involves traditional trial-and-error methods using physical perceptions and parametric research. This approach is inefficient and time-consuming, potentially resulting in ineffective designs.
Numerical techniques like finite difference, finite element, block-iterative frequency-domain, and plane wave expansion methods are commonly used for precise simulation and optimization of PC structures. However, these techniques become computationally intensive because complex PC structures require numerous iterations for an optimal solution.2
Recent Technological Advancements in PCs
Significant efforts are being made to enhance PCs' functionality and practical deployment in research and drug discovery. For instance, a recent study in Smart Medicine explored magnetic PCs for biomedical applications. Magnetic PCs, with their contactless functioning, adaptable orientations, and variable magnetic field intensity, are highly suitable for bioimaging and auxiliary clinical diagnosis.
Magnetic PCs are effective contrast agents in magnetic resonance imaging (MRI) due to their tunable sizes, amenable paramagnetism, instant responsiveness, and high biocompatibility. Additionally, their magnetothermal properties are essential tools for tumor thermotherapy.3
Another recent article in Nano Research highlighted advances in multifunctional shape memory PCs (SMPCs) and their potential biomedical applications. SMPCs are smart composites of integrated shape memory polymers and PCs.
These materials can transform into temporary shapes by nanoscale deformation and recover to the initial or intermediate state due to external stimuli, along with a change in structural color. As porous materials with inherent sensing capabilities, SMPCs can accelerate biomedical research advancements.4
Future Outlook and Potential Impact of PCs
Stimuli-responsive PCs have wide applications in drug delivery implants, allowing control of drug release according to electrical or thermal stimuli from the patient and real-time monitoring of the process. These attributes make functional PC materials ideal candidates for novel implantable devices, potentially replacing traditional treatments and improving drug safety and efficacy.1
Deep learning and other artificial intelligence algorithms are transforming the design, integration, and measurement of photonics. They have enormous potential to optimize the design, structure, material choice, and functionality of PCs and PC-based biomedical systems.2
Future PC-based sensors with better controllability, integration, design, and programmable functionalities can accelerate drug discovery processes and serve advanced diagnostic tools, potentially leading to breakthroughs in treatment methods and personalized medicine.2,3
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References and Further Reading
1. Chen, H., Lou, R., Chen, Y., Chen, L., Lu, J., Dong, Q. (2017). Photonic crystal materials and their application in biomedicine. Drug Delivery. doi.org/10.1080/10717544.2017.1321059
2. Mohammed, NA., Khedr, OE., El-Rabaie, E.-SM., Khalaf, AAM. (2022). Literature Review: On-Chip Photonic Crystals and Photonic Crystal Fiber for Biosensing and Some Novel Trends. IEEE Access. doi.org/10.1109/access.2022.3170912
3. Chen, H., Li, N., Gu, Z., Gu, H., Wang, J. (2023). Magnetic photonic crystals for biomedical applications. Smart Medicine. doi.org/10.1002/smmd.20220039
4. Qi, Y., Zhang, S. (2023). Recent advances in multifunctional shape memory photonic crystals and practical applications. Nano Research. doi.org/10.1007/s12274-023-5801-0
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