With the rapid advancement in “noninvasive” imaging technologies and imaging probes, the field of imaging science is growing exponentially. A variety of functional nanoparticles, such as gold nanoparticles, superparamagnetic nanoparticles, quantum dots, and rare earth upconverting nanoparticles, have gained much attention as imaging agents for next generation diagnostics tools, due to their superior photostability, narrow range of emission, broad excitation wavelength and multiple possibilities of modification.
Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI) images organs and structures inside the body using a magnetic field and pulses of radio wave energy. When the nuclei of protons are exposed to a strong magnetic field, their spins align parallel or antiparallel to the magnetic field, which presents a resonance frequency (Larmor Frequency). In this way, protons absorb energy and are excited to the antiparallel state. Finally, the excited nuclei relax to initial lower-energy state by longitudinal (T1) or transverse (T2) relaxation. Based on nuclear magnetic resonance along with the relaxation of proton spins in a magnetic field, these signal is recorded and converted to a picture.
Various inorganic nanoparticles have been used as MRI contrast agents due to their unique properties, such as large surface area and efficient contrasting effect. Typically, magnetic iron oxide nanoparticles have been extensively used due to their ability to shorten transverse relaxation times in the liver, spleen, and bone marrow, which can function as both contrast agents for imaging and drug delivery vehicles for treating brain tumors.
Recent research has been conducted to develop nanoparticle-based T1 contrast agents, such as nanostructure immobilized Gadolinium complexes, to overcome the drawbacks of iron oxide nanoparticle-based negative T2 contrast agents. Moreover, some new types of nanoparticles contrast agents are developed, which are composed of three parts: the core parts for signal enhancement, the water-dispersible shells for increasing biocompatibility, and the bioactive materials for targeting purpose. Future studies will focus on how to use these nanoparticle contrast agents in real clinic diagnosis.
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Computed Tomography (CT)
Computed Tomography (CT) is a whole-body imaging technique imaging based on the absorption of X-rays when they pass through the different parts of the body. Depending on the amount absorbed in a particular tissue, some of X-rays pass through and exit the body, resulting in a different form of imaging known as cross-sectional imaging. Small iodinated molecules are generally used as CT contrast agents. However, these contrast agents typically exhibit rapid renal excretion and allow very short time imaging.
Nanoparticles such as iodine-based nanoparticles are expected to be the next generation contrast agents in CT due to their advantages over the conventional contrast agents. Nanoparticles usually show a longer blood circulation time, potential for cell tracking and specific molecular targeting capabilities. Moreover, metallic nanoparticles have attracted much attention as CT contrast agents for the detection of cells and tissues due to their strong X-ray absorption ability. For example, various contrast agents based on gold nanoparticles have been developed and are expected to improve X-ray imaging technologies in different sides, including three-dimensional biological imaging, dynamical processes in a living system and quantitative analysis of circulatory systems.
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| DiagNano™ Gold Nanoparticles, 20 nm |
| DiagNano™ Stabilized Gold Nanoparticles, 20 nm |
| DiagNano™ Ultrapure Gold Nanoparticles, 20 nm |
| DiagNano™ Silica-Coated Gold Nanoparticles, 20 nm |
| DiagNano™ Silica-Coated PEGylated Gold Nanoparticles, 20 nm |
| DiagNano™ Methyl, PEG2000 Gold Nanoparticles, 20 nm |
| DiagNano™ Carboxyl, PEG3000 Gold Nanoparticles, 20 nm |
| DiagNano™ Amine, PEG3000 Gold Nanoparticles, 20 nm |
| DiagNano™ Biotin, PEG5000 Gold Nanoparticles, 20 nm |
Positron Emission Tomography (PET)
Positron emission tomography (PET) is a diagnostic modality that can noninvasively survey the entire body and sensitively detect various cancers. PET detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three-dimensional images of tracer concentration within the body are then constructed by computer analysis.
Nanoparticles have been extensively explored to improve the PET technology. The structure of the nanoparticles allows a broad range of radio-labeled chemistries to be used to attach various PET nuclides to the particle. Besides, the nanoparticles for targeted imaging have more promising attributes, including their ability to deliver large numbers of imaging agents to achieve high-sensitivity imaging. The primary challenges in the future will be the development of nanoparticles conjugated tracers and to accomplish truly in-vivo tissue-selective targeting.
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Near-Infrared (NIR) Fluorescent Imaging
Near infrared imaging (NIR) has proved to be a powerful diagnostic technique with the potential method for sensitive deep tissue diagnostic imaging. In spite of characterization function in material science, the widest application of NIR imaging is the medical use. One of the applications of NIR imaging is to determinate absorption coefficients and measure the location and activity of specific regions of the brain by continuously monitoring blood hemoglobin levels. Besides, NIR can also be used as a quick screening tool for possible intracranial bleeding cases or served as a non-invasive assessment tool for brain function.
Nanoparticles based near infrared (NIR) contrast agents are resisted to the rapid photobleaching and photoblinking. Some nanoparticles, such as quantum dots and upconverting nanoparticles, have been demonstrated as reliable agents for the next generation of NIR imaging technology.
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Functional Quantum Dots
Quantum Dots Labeling & Conjugation Kits
Ultrasound Imaging is a diagnostic imaging technique based on high-frequency sound waves to view inside of the body. Ultrasound images are captured in real-time, so they can show a movement of the body's internal organs as well as blood flowing through the blood vessels. Besides, Ultrasound is safe and painless, there is no radiation exposure associated with ultrasound imaging.
Some nanoparticles offer help as contrast agents to detect the very earliest stages of cancer by ultrasound imaging. It has been demonstrated that not only can ultrasound waves sense nanoparticles, but the nanoparticles can brighten the resulting image. For example, silica nanoparticles have an effect on boosting reflection of ultrasonic energy when it passes through the body.
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