Bioconjugation in Nanotechnology

Nanomaterials, due to their small size and large surface area, exhibit unique physical and chemical properties that can be exploited for various applications. Bioconjugation technology plays a pivotal role in nanotechnology by combining functional biomolecules with nanomaterials to achieve precise control and functionalization of nanostructures. When combined with the specificity and functionality of biomolecules, these nanomaterials can be tailored for specific tasks such as targeted therapy, biosensing, and environmental monitoring. Bioconjugation ensures that the biomolecules retain their biological activity and functionality when attached to the nanomaterial surfaces, allowing for the development of highly effective and specialized nanodevices. This fusion of biological and nanotechnological advancements has paved the way for innovative applications in medicine, environmental science, and various industrial sectors. By leveraging bioconjugation, researchers can enhance the capabilities of nanomaterials, creating sophisticated systems for targeted drug delivery, advanced diagnostics, and responsive environmental sensors.

Types of Nanomaterials in Bioconjugation

Bioconjugation is employed to modify the surfaces of nanoparticles for different applications and purposes. These techniques involve attaching fluorescent markers, targeting molecules, or therapeutic agents to various nanoparticles, enhancing their utility in biological labeling, drug delivery, or cell-targeted therapies.

Quantum Dots

Quantum dots are a new type of nanomaterial that can be varied to fit a specific purpose depending on their functionalization. They are semiconducting nanoparticles that have interesting optical and electronic properties as well as high stability. They can be used as fluorescent probes for imaging biomolecules because of their high stability. However, quantum dots can be highly toxic, which is less useful in imaging applications when you are monitoring a living organism. Quantum dots can be conjugated with fluorescent dyes or proteins, enabling their use in cellular imaging and tracking. These fluorescently labeled nanoparticles provide bright and stable signals, allowing researchers to visualize and study cellular processes with high resolution and sensitivity.

Fluorescence micrographs of QD-stained cells and tissues. (Zhao M X., et al., 2015)

DNA nanostructures

There are many different kinds of DNA nanostructures and also have been used to oligonucleotide delivery. These structures include DNA origami, which uses short DNA "nails" to hold long DNA molecules in defined structures, resulting in a wide variety of complex shapes, including polygonal nanostructures such as DNA cages. DNA nanostructures is usually due to its component of the complementary base pairing and self-assembly, and can be designed to have a precise geometry, can be designed to be small (~ 20 nm). Application for nucleic acid delivery of DNA nanostructures is usually the nucleic acid drug (and aptamer targeting ligands) incorporated in the structure design range of modular structure itself.

Self-assembled DNA cage tetrahedron nanostructure. (Roberts T C., et al., 2020)

Lipoplexes and liposomes

Lipid formulation is one of the most common methods use to enhance nucleic acid delivery. Bioconjugate polyanionic nucleic acid drugs with lipids results in the bioconjugation of nucleic acids into nanoparticles that have a more favorable surface charge and are large enough (~ 100 nm in diameter) to trigger endocytic uptake. Lipid compounds are polyanionic and cationic lipid nucleic acid directly the result of the electrostatic interaction between heterogeneous populations is usually relatively unstable compounds. Positive liposome /DNA complex preparations need to be prepared shortly before use and have been successfully used in topical delivery applications. In contrast, liposomes contain lipid bilayers and nucleic acid drugs exist in encapsulated aqueous Spaces.

Liposomes are more complex than lipoplexes, typically consisting of cationic or fusion lipids and cholesterol PEGylated lipids, and exhibit more consistent physical properties and higher stability. For example, some lipid nanoparticles (LNPs), also known as stable nucleic acid lipid particles, are liposomes that contain ionizable lipid, phosphatidylcholine, cholesterol and PEG–lipid conjugates in defined ratios and have been successfully utilized in multiple instances.

Stable nucleic acid lipid particle encapsulating siRNAs. (Roberts T C., et al., 2020)

Exosome

An area of nanotechnology that is gaining interest is based on the application of natural biological

nanoparticles known as exosomes (a class of extracellular vesicles). Exosomes are heterogeneous, lipid bilayer-encapsulated vesicles approximately 100 nm in diameter that are generated as a result of the inward budding of the multivesicular bodies. Exosomes are thought to be released into the extracellular space by all cells, where they facilitate intercellular communication via the transfer of their complex macromolecular cargoes (that is, nucleic acids, proteins and lipids).

The pattern of exosome biodistribution can be favourably altered through the display of surface ligands, such as peptides like rabies virus glycoprotein (RVG) to enhance brain penetration and facilitate delivery to cells within the nervous system or GE11 that promotes binding to tumor cells by interacting with EGFR. Similarly, exosomes decorated with an RNA aptamer targeting PSMA (prostate-specific membrane antigen) were capable of delivering siRNAs to xenograft tumors and inducing tumor regression.

Engineered exosome with the brain-targeting rabies virus glycoprotein (RVG) peptide displayed on the outer surface. (Roberts T C., et al., 2020)

Spherical nucleic acids (SNA)

Spherical nucleic acids (SNA) approach is also an alternative nanoparticle-based delivery method. SNA particles consist of a hydrophobic core nanoparticle (comprising gold, silica or various other materials) that is decorated with hydrophilic oligonucleotides (for example, ASOs, siRNAs and immunostimulatory oligonucleotides) that are densely packed onto the surface via thiol linkages. In contrast to other nanoparticle designs, SNA-attached oligonucleotides radiate outwards from the core structure. While exposed, the oligonucleotides are protected from nucleolytic degradation to some extent as a consequence of steric hindrance, high local salt concentration, and through interactions with corona proteins.

Spherical nucleic acid nanoparticle consisting of a gold core coated in densely packed ASOs attached by metal–thiol linkages. (Roberts T C., et al., 2020)

Advantages and Features of Bioconjugation in Nanotechnology

Bioconjugation technology offers several advantages and features that enhance the performance and applicability of nanomaterials in various fields:

High Specificity: Bioconjugation ensures the specific attachment of biomolecules to nanomaterials, enabling targeted interactions and functions. This specificity is crucial for developing effective biosensors, targeted therapies, and diagnostic tools.

Stability: The covalent bonds formed during bioconjugation provide strong and stable attachment of biomolecules to nanomaterials, ensuring the stability and durability of the bioconjugates. This stability is essential for maintaining the functionality of nanomaterials in various applications, including long-term storage and use in harsh environments.

Enhanced Performance: By combining the unique properties of nanomaterials with the functionality of biomolecules, bioconjugation enhances the performance of nanomaterials in biomedical and environmental applications. This enhancement can lead to improved sensitivity, specificity, and efficiency in various applications, such as biosensing and drug delivery.

Controlled Functionalization: Bioconjugation allows for precise control over the functionalization of nanomaterials, enabling the creation of highly specialized and tailored systems. This control is important for optimizing the performance and effectiveness of nanomaterials in specific applications, such as creating multifunctional nanoparticles for simultaneous imaging and therapy.

Applications of Bioconjugation in Nanotechnology

Bioconjugation plays a pivotal role in the field of nanotechnology, enhancing the functionality and specificity of nanoparticles for a wide range of applications. Here are some key applications:

Biosensing

In nanotechnology, bioconjugation is widely used to develop highly sensitive and specific biosensors. These sensors can detect a wide range of biological molecules, including proteins, nucleic acids, and small molecules, at very low concentrations. For instance, gold nanoparticles conjugated with antibodies can be used to create immunosensors that detect specific antigens with high sensitivity and specificity. These biosensors are valuable tools for disease diagnostics, environmental monitoring, and food safety testing.

Drug Delivery

Bioconjugation facilitates the development of advanced drug delivery systems that target specific cells or tissues. By conjugating therapeutic agents to nanoparticles, researchers can create delivery systems that improve the bioavailability, stability, and targeting of drugs. For example, liposomes conjugated with targeting ligands can deliver anticancer drugs specifically to tumor cells, minimizing side effects and improving therapeutic outcomes. Similarly, polymer nanoparticles conjugated with drugs can provide controlled and sustained release, enhancing the efficacy and safety of treatments.

Molecular Imaging

Bioconjugation enables the creation of nanoparticles with enhanced imaging capabilities, improving the resolution and sensitivity of molecular imaging techniques. For instance, quantum dots conjugated with fluorescent dyes can be used for cellular imaging, allowing researchers to visualize and track cellular processes with high resolution. Similarly, magnetic nanoparticles conjugated with contrast agents can enhance the sensitivity of magnetic resonance imaging (MRI), providing detailed images of tissues and organs for disease diagnosis and monitoring.

Bioanalysis

Bioconjugation is used to develop advanced bioanalytical tools that enable the precise analysis of biological molecules and processes. These tools include nanoparticle-based assays and sensors that detect and quantify biomolecules with high sensitivity and specificity. For example, nanoparticles conjugated with enzymes can be used to create colorimetric assays that detect specific substrates, providing rapid and accurate measurements for research and diagnostics. Additionally, nanoparticles conjugated with nucleic acids can be used for DNA sequencing and genotyping, offering powerful tools for genetic analysis.

Environmental Applications

In environmental science, bioconjugation is used to develop sensors and systems for detecting and monitoring pollutants and toxins. Nanoparticles conjugated with biomolecules can be used to create sensors that detect specific contaminants in water, air, and soil with high sensitivity and specificity. For instance, nanoparticles conjugated with enzymes can be used to create biosensors that detect pesticides or heavy metals in water, providing valuable tools for environmental monitoring and protection.

Future Prospects

The future of bioconjugation in nanotechnology is promising, with several exciting trends and developments on the horizon:

Technological Innovation: Ongoing advancements in Bioconjugation and nanomaterials will enable the creation of more sophisticated and efficient nanodevices. Innovations such as bioorthogonal chemistry, click chemistry, and site-specific conjugation will enhance the precision and versatility of bioconjugation in nanotechnology.

Integration with Advanced Technologies: Combining bioconjugation with emerging technologies such as microfluidics, single-molecule spectroscopy, and super-resolution microscopy will enable more detailed and precise studies of biological processes. These integrated approaches will allow researchers to investigate the behavior and interactions of biomolecules and nanomaterials at unprecedented resolution and sensitivity.

Personalized Medicine: Bioconjugation will drive the development of personalized medicine approaches, enabling the creation of tailored diagnostic and therapeutic systems. By leveraging bioconjugation, researchers can develop nanomaterials that target specific disease markers or patient-specific biomolecules, improving the efficacy and safety of treatments.

Sustainable Development: Bioconjugation will contribute to sustainable development by enabling the creation of eco-friendly nanomaterials and processes. This technology will support the development of renewable energy solutions, pollution control systems, and resource-efficient manufacturing processes.

Multifunctional Nanodevices: The development of multifunctional nanodevices that combine imaging, targeting, and therapeutic capabilities will revolutionize biomedical research and healthcare. These devices will offer powerful tools for disease diagnosis, monitoring, and treatment, providing new solutions for complex medical challenges.

In Vivo Applications: Developing in vivo Bioconjugation will enable the study of biological processes within living organisms, providing more relevant and accurate insights. In vivo bioconjugation will allow researchers to track and analyze biomolecules and nanomaterials in their natural context, enhancing our understanding of dynamic biological processes and improving the development of targeted therapies.