Immobilization mechanisms of deoxyribonucleic acid (DNA) to hafnium dioxide (HfO2) surfaces for biosensing applications

Synthesis and Bioapplication of Emerging Nanomaterials of Hafnium

A significant amount of progress in nanotechnology has been made due to the development of engineered nanoparticles. The use of metallic nanoparticles for various biomedical applications has been extensively investigated. Biomedical research is highly focused on them because of their inert nature, nanoscale structure, and similar size to many biological molecules. The intrinsic characteristics of these particles, including electronic, optical, physicochemical, and surface plasmon resonance, that can be altered by altering their size, shape, environment, aspect ratio, ease of synthesis, and functionalization properties, have led to numerous biomedical applications. Targeted drug delivery, sensing, photothermal and photodynamic therapy, and imaging are some of these. The promising clinical results of NBTXR3, a high-Z radiosensitizing nanomaterial derived from hafnium, have demonstrated translational potential of this metal. This radiosensitization approach leverages the dependence of energy attenuation on atomic number to enhance energy-matter interactions conducive to radiation therapy. High-Z nanoparticle localization in tumor issue differentially increases the effect of ionizing radiation on cancer cells versus nearby healthy ones and mitigates adverse effects by reducing the overall radiation burden. This principle enables material multifunctionality as contrast agents in X-ray-based imaging. The physiochemical properties of hafnium (Z = 72) are particularly advantageous for these applications. A well-placed K-edge absorption energy and high mass attenuation coefficient compared to elements in human tissue across clinical energy ranges leads to significant attenuation. Chemical reactivity allows for variety in nanoparticle synthesis, composition, and functionalization. Nanoparticles such as hafnium oxide exhibit excellent biocompatibility due to physiochemical inertness prior to incidence with ionizing radiation. Additionally, the optical and electronic properties are applicable in biosensing, optical component coatings, and semiconductors. The wide interest has prompted extensive research in design and synthesis to facilitate property fine-tuning. This review summarizes synthetic methods for hafnium-based nanomaterials and applications in therapy, imaging, and biosensing with a mechanistic focus. A discussion and future perspective section highlights clinical progress and elaborates on current challenges. By focusing on factors impacting applicational effectiveness and examining limitations this review aims to support researchers and expedite clinical translation of future hafnium-based nanomedicine.

Nature-Inspired Stalactite Nanopores for Biosensing and Energy Harvesting

Nature provides a wide range of self-assembled structures from the nanoscale to the macroscale. Under the right thermodynamic conditions and with the appropriate material supply, structures like stalactites, icicles, and corals can grow. However, the natural growth process is time-consuming. This work demonstrates a fast, nature-inspired method for growing stalactite nanopores using heterogeneous atomic deposition of hafnium dioxide at the orifice of templated silicon nitride apertures. The stalactite nanostructures combine the benefits of reduced sensing region typically for 2-dimensional material nanopores with the asymmetric geometry of capillaries, resulting in ionic selectivity, stability, and scalability. The proposed growing method provides an adaptable nanopore platform for basic and applied nanofluidic research, including biosensing, energy science, and filtration technologies.

Hardness, Modulus, and Refractive Index of Plasma-Assisted Atomic-Layer-Deposited Hafnium Oxide Thin Films Doped with Aluminum Oxide

Coatings with tunable refractive index and high mechanical resilience are useful in optical systems. In this work, thin films of HfO₂ doped with Al₂O₃ were deposited on silicon at 300 °C by using plasma-enhanced atomic layer deposition (PE-ALD). The mainly amorphous 60-80 nm thick films consisted Al in the range of 2 to 26 at.%. The refractive indexes varied from 1.69 to 2.08 at the wavelength of 632 nm, and they consistently depended on the composition. The differences were higher in the UV spectral region. At the same time, the hardness of the films was from 12-15 GPa; the modulus was in the range of 160-180 GPa; and the mechanical properties did not have a good correlation with the deposited compositions. The deposition conditions, element contents, and refractive indexes at respective wavelengths were correlated. The results indicated that it is possible to tune optical properties and retain mechanical properties of atomic layer-deposited thin films of HfO₂ with Al₂O₃ as doping oxide. Such films could be used as mechanically resilient and optically tunable coatings in, for instance, micro- or nano-electromechanical systems or transparent displays.

Use of hafnium(IV) oxide in biosensors

Hafnium(IV) oxide is a material with properties that can increase the sensitivity, durability, and reliability of biosensors made from silicon dioxide and other semiconductor materials due to its high dielectric constant, thermodynamic stability, and the simplicity with which it can be deposited. This work describes the use of this material in biosensors based on field-effect transistors to detect ions and DNA, in immunosensors to detect an antigen-antibody complex, its use as a contrast material in computed tomography scans and the possibility of using it in optic biosensors in the infrared region. Its low cost and versatility in the field of biosensors is underscored.

A novel approach to low-temperature synthesis of cubic HfO2 nanostructures and their cytotoxicity

The development of a strategy to stabilise the cubic phase of HfO₂ at lower temperatures is necessary for the emergence of unique properties that are not realised in the thermodynamically stable monoclinic phase. A very high temperature (>2600 °C) is required to produce the cubic phase of HfO₂, whereas the monoclinic phase is stable at low temperature. Here, a novel rapid synthesis strategy was designed to develop highly crystalline, pure cubic-phase HfO₂ nanoparticles (size <10 nm) using microwave irradiation. Furthermore, the as-prepared nanoparticles were converted to different morphologies (spherical nanoparticles and nanoplates) without compromising the cubic phase by employing a post-hydrothermal treatment in the presence of surface modifiers. The cytotoxicities and proliferative profiles of the synthesised cubic HfO₂ nanostructures were investigated over the MCF-7 breast cancer cell line, along with caspase-3/7 activities. The low-temperature phase stabilisation was significantly attributed to surface imperfections (defects and deformations) induced in the crystal lattice by the desirable presence of Na₂S·xH₂O and NaOH. Our work provides unprecedented insight into the stabilisation of nanoscale cubic-phase HfO₂ in ambient environments; the method could be extended to other challenging phases of nanomaterials.

Comprehensive Screen of Metal Oxide Nanoparticles for DNA Adsorption, Fluorescence Quenching, and Anion Discrimination

Although DNA has been quite successful in metal cation detection, anion detectioin remains challenging because of the charge repulsion. Metal oxides represent a very important class of materials, and different oxides might interact with anions differently. In this work, a comprehensive screen of common metal oxide nanoparticles (MONPs) was carried out for their ability to adsorb DNA, quench fluorescence, and release adsorbed DNA in the presence of target anions. A total of 19 MONPs were studied, including Al2O3, CeO2, CoO, Co3O4, Cr2O3, Fe2O3, Fe3O4, In2O3, ITO, Mn2O3, NiO, SiO2, SnO2, a-TiO2 (anatase), r-TiO2 (rutile), WO3, Y2O3, ZnO, ZrO2. These MONPs have different DNA adsorption affinity. Some adsorb DNA without quenching the fluorescence, while others strongly quench adsorbed fluorophores. They also display different affinity toward anions probed by DNA desorption. Finally, CeO2, Fe3O4, and ZnO were used to form a sensor array to discriminate phosphate, arsenate, and arsenite from the rest using linear discriminant analysis. This study not only provides a solution for anion discrimination using DNA as a signaling molecule but also provides insights into the interface of metal oxides and DNA.

Straightforward Micropatterning of Oligonucleotides in Microfluidics by Novel Spin-On ZrO₂ Surfaces

DNA biochip assays often require immobilization of bioactive molecules on solid surfaces. A simple biofunctionalization protocol and precise spatial binding represent the two major challenges in order to obtain localized region specific biopatterns into lab-on-a-chip (LOC) systems. In this work, a simple strategy to anchor oligonucleotides on microstructured areas and integrate the biomolecules patterns within microfluidic channels is reported. A photosensitive ZrO2 system is proposed as an advanced platform and versatile interface for specific positioning and oriented immobilization of phosphorylated DNA. ZrO2 sol-gel structures were easily produced on fused silica by direct UV lithography, allowing a simple and fast patterning process with different geometries. A thermal treatment at 800 °C was performed to crystallize the structures and maximize the affinity of DNA to ZrO2. Fluorescent DNA strands were selectively immobilized on the crystalline patterns inside polydimethylsiloxane (PDMS) microchannels, allowing high specificity and rapid hybridization kinetics. Hybridization tests confirmed the correct probe anchoring and the bioactivity retention, while denaturation experiments demonstrated the possibility of regenerating the surface.

Genotoxicity of metal oxide nanomaterials: review of recent data and discussion of possible mechanisms

Nanotechnology has rapidly entered into human society, revolutionized many areas, including technology, medicine and cosmetics. This progress is due to the many valuable and unique properties that nanomaterials possess. In turn, these properties might become an issue of concern when considering potentially uncontrolled release to the environment. The rapid development of new nanomaterials thus raises questions about their impact on the environment and human health. This review focuses on the potential of nanomaterials to cause genotoxicity and summarizes recent genotoxicity studies on metal oxide/silica nanomaterials. Though the number of genotoxicity studies on metal oxide/silica nanomaterials is still limited, this endpoint has recently received more attention for nanomaterials, and the number of related publications has increased. An analysis of these peer reviewed publications over nearly two decades shows that the test most employed to evaluate the genotoxicity of these nanomaterials is the comet assay, followed by micronucleus, Ames and chromosome aberration tests. Based on the data studied, we concluded that in the majority of the publications analysed in this review, the metal oxide (or silica) nanoparticles of the same core chemical composition did not show different genotoxicity study calls (i.e. positive or negative) in the same test, although some results are inconsistent and need to be confirmed by additional experiments. Where the results are conflicting, it may be due to the following reasons: (1) variation in size of the nanoparticles; (2) variations in size distribution; (3) various purities of nanomaterials; (4) variation in surface areas for nanomaterials with the same average size; (5) differences in coatings; (6) differences in crystal structures of the same types of nanomaterials; (7) differences in size of aggregates in solution/media; (8) differences in assays; (9) different concentrations of nanomaterials in assay tests. Indeed, due to the observed inconsistencies in the recent literature and the lack of adherence to appropriate, standardized test methods, reliable genotoxicity assessment of nanomaterials is still challenging.

DNA adsorption by indium tin oxide nanoparticles

The high conductivity and optical transparency of indium tin oxide (ITO) has made it a popular material in the electronic industry. Recently, its application in biosensors is also explored. To understand its biointerface chemistry, we herein investigate its interaction with fluorescently labeled single-stranded oligonucleotides using ITO nanoparticles (NPs). The fluorescence of DNA is efficiently quenched after adsorption, and the interaction between DNA and ITO NPs is strongly dependent on the surface charge of ITO. At low pH, the ITO surface is positively charged to afford a high DNA adsorption capacity. Adsorption is also influenced by the sequence and length of DNA. For its components, In2O3 adsorbs DNA more strongly while SnO2 repels DNA at neutral pH. The DNA adsorption property of ITO is an averaging result from both components. DNA adsorption is confirmed to be mainly by the phosphate backbone via displacement experiments using free phosphate or DNA bases. Last, DNA-induced DNA desorption by forming duplex DNA is demonstrated on ITO, while the same reaction is more difficult to achieve on other metal oxides including CeO2, TiO2, and Fe3O4 because these particles adsorb DNA more tightly.

Slow DNA transport through nanopores in hafnium oxide membranes

We present a study of double- and single-stranded DNA transport through nanopores fabricated in ultrathin (2-7 nm thick) freestanding hafnium oxide (HfO2) membranes. The high chemical stability of ultrathin HfO2 enables long-lived experiments with <2 nm diameter pores that last several hours, in which we observe >50 000 DNA translocations with no detectable pore expansion. Mean DNA velocities are slower than velocities through comparable silicon nitride pores, providing evidence that HfO2 nanopores have favorable physicochemical interactions with nucleic acids that can be leveraged to slow down DNA in a nanopore.

Peptide nucleic acid (PNA)-DNA duplexes: comparison of hybridization affinity between vertically and horizontally tethered PNA probes

We compare the PNA-DNA duplex hybridization characteristics of vertically tethered and new horizontally tethered PNA probes on solid surfaces. The horizontal 15-mer PNA probe has been synthesized with linker molecules attached at three locations (γ-points) positioned along the PNA backbone that provides covalent attachment of the probe with the backbone aligned parallel to the surface, which is important for DNA hybridization assays that use electric field effect sensors for detection. A radioactive labeled assay and real-time surface plasmon resonance (SPR) biosensor are used to assess the probe surface density, nonspecific binding, and DNA hybridization affinity, respectively, of the new PNA probe configuration. The estimated equilibrium dissociation constants of the horizontally tethered duplex and the vertically tethered duplex are of the same order of magnitude (KD ≈ 5 nM), which indicates a sufficient hybridization affinity for many electronic biosensors that benefit from the horizontal alignment, which minimizes the effects of counterion screening.