Upconversion nanoparticles (UCNP) have shown broad application prospects in the fields of biosensing and bioimaging. Upconversion nanoparticles are mainly obtained by doping trivalent rare earth ions (such as Er3+, Eu3+, Yb3+, Tm3+, Ho3+, etc.) in oxide, fluoride, oxyhalide and other matrices. Their unique feature is that they can continuously absorb two or more pump photons are converted into light with a shorter wavelength than the pump light, that is, low-energy light is converted into high-energy light. This characteristic gives UCNPs significant advantages in the field of biosensing and imaging, including low toxicity, stable chemical properties, no light flickering, resistance to degradation and photobleaching, low background fluorescence, and deep light penetration depth.
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In terms of biosensing, the applications of UCNPs include the construction of biosensors based on the fluorescence resonance energy transfer (FRET) principle for the detection of biomolecules such as lysozyme, cholesterol, and specific DNA sequences. The application of this material in biosensing is mainly reflected in the following aspects:
Biomolecule detection: UCNPs can be used to construct biosensors for detecting specific biomolecules, such as lysozyme, cholesterol, etc. Through the principle of fluorescence resonance energy transfer (FRET), UCNPs can serve as energy donors and combine with dye molecules or gold nanoparticles as acceptors to achieve highly sensitive detection of specific biomolecules. This method has low detection limit, high selectivity and good repeatability, providing a new means for quantitative detection of biomolecules. For example, by synthesizing NaYF4, Er and connecting UCNPs and nucleic acid aptamers through cationic polymers, a simple biosensor was constructed for detecting lysozyme and target DNA. This method is not only simple and convenient, but also avoids complicated modification steps, and has certain reference value for the determination of biomolecules.
Virus diagnosis: UCNPs also show good performance in virus diagnosis. Their high stability, low fluorescence background, low toxicity and resistance to photobleaching are beneficial to improving detection sensitivity. The multicolor emission and narrow emission band of UCNPs enable a variety of biological detections while avoiding interference from different fluorescence signals, providing new tools and methods for virus diagnosis.
Molecular Recognition and Separation: Combined with molecularly imprinted polymers (MIPS), UCNPs can be used in composite materials for molecular recognition, sensing or separation. UCNPs provide optical sensitivity, while the MIPS part provides molecular selectivity. This composite material has potential application value in chemical sensing, molecular separation and other fields.
In the field of biological imaging, the applications of UCNPs include multi-modal imaging, such as combining CT, MR, PET and other technologies to obtain clear images with high signal-to-noise ratio. UCNPs have excellent optical stability, high chemical stability, low toxicity, deep tissue penetration ability under near-infrared light excitation, no damage to biological tissues, and nearly zero background fluorescence interference, making them widely used in biomedical imaging. It has broad application prospects.
In order to improve the application effect of upconversion nanoparticles in biological imaging, research focuses on improving the quantum efficiency of upconversion, increasing the absorption cross-section, improving water solubility, and further functionalization. For example, by using NaLuF4 as the matrix and doping with Er or Tm, strong upconversion luminescence can be obtained. Doping with Gd3+ can induce the α phase to β phase, and the particle size is also reduced. Finally, The obtained rare earth upconversion nanoparticles of about 7.8 nm have a quantum efficiency of up to 0.47%, which is higher than the upconversion nanomaterial currently recognized as the best hexagonal phase NaYF4 as a matrix.
In addition to their applications in fluorescence imaging, upconversion nanoparticles can also be used as drug carriers to reach pathological locations through targeting and perform visual monitoring. In addition, upconversion nanoparticles can also be used as probes for other imaging technologies, but they have shortcomings such as low tissue penetration depth and insufficient luminous efficiency. Therefore, how to prepare high penetration depth, high luminous efficiency, good dispersion, and morphology Size-controllable multimodal bioimaging probes have become a key issue.
In addition, UCNPs have also been studied for photodynamic therapy (PDT). Although there are some shortcomings in the application process, such as low energy transfer efficiency, overheating of normal tissues, etc. This shows that the application of UCNPs in the biomedical field is not limited to imaging and sensing, but also extends to the therapeutic field.
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