# Carbon Nanoparticles and Their Biomedical Applications
## 2 Bioimaging, Detection, and Diagnostics of Various Pathologies  
Early and accurate diagnoses are essential for treatment outcomes, whether it is the detection of damaged tissue or cancer. CNPs can significantly improve the quality of medical imaging. Most CNPs have the natural ability to emit fluorescence upon photoexcitation [17; 18]. Carbon dots, graphene quantum dots, and carbon nanotubes are widely used. Lastly, the 'named' has an ultra-large surface and can carry multiple molecules and ensure multiplex sensing; on the other hand, CNPs with fast excretion via the kidney or hepatobilary system (carbon dots under 10 nm) are suitable for bioimaging [19]. Based on the different nanostructures and functionalization of CNPs, the individual organelles and cells can be imaged and the fluorescence can be targeted. After intravenous application in mice, the functionalized carbon dots rapidly move into the tissue and accumulate in the lung, liver, and kidney, but also cross the blood-brain barrier [20]. The M13 virus coated with single-wall carbon nanotubes can especially target the tumor cells. Additionally, radionuclide-labeled particles (Technietium-99 m Tc) target tumors and are detectable by positron emission tomography (PET) [21; 22]. These methods can combine the fluorescence effect of CNPs with medical imaging techniques, such as computed tomography (CT), magnetic resonance imaging (MRI), or PET. This combination enhances the quality and sensitivity of imaging and displays more details with better contrast [23]. The use of CNPs also allows deep-tissue optical imaging by near-infrared optical imaging. The near-infrared system (NIR-II; 1000-1700 nm) has shown a deeper penetration depth and, therefore, can explore deep tissue information with higher resolution and no  
Figure 2: Application of CNPs. autofluorescence. The benefits include whole body and brain angiography (visualization of blood flow, microcirculation), visualization of organs, and imaging-guided cancer therapy or surgery [24; 25]. The practical intraoperative use of CNPs is well documented. [PERSON] et al. studied the transport and accumulation of CNPs (mean 150 nm) into the lymph nodes of patients with advanced gastric cancer during gastrectomy with lymph node dissection. Identification/staining of metastatic lymph nodes is essential to reduce the risk of cancer recurrence. Thirty patients participated in the study. No serious adverse reactions were documented after intravenous application. CNPs accumulated selectively in the draining lymph nodes and colored them black. This method could detect the smaller lymph nodes; thus, the number of potentially dangerous lymph nodes was higher [26]. The same effect has been documented in the preoperative and perioperative detection of lymph nodes in patients with thyroid, colorectal, and breast cancer [27; 28; 29]. In thyroid cancer, CNPs help discriminate lymph nodes and parathyroid glands [30]. Importantly, CNPs used for endoscopic tattooing of colorectal cancer allow the detection and precise localization of tumors and precancerous lesions before and during surgery. This allows an accurate resection to be performed and, thus, reduces surgical trauma [31]. Interestingly, nanodiamond nanoparticles with silicon-vacancy centers can easily be up-taken by cells and, thus, can be used for live-cell dual-color imaging and intracellular tracking. They have shown greater photostability and narrow emissions in the near-infrared region [32]. Graphene and graphene-based nanomaterials can be used to detect the neural interface. [PERSON] et al. created a sensing system composed of a flexible 64-channel graphene solution-gated field-effect transistor array and a wireless headstage. In vivo, they performed 24-h quasi-continuous monitoring of brain activity to assess the sensitivity of the method. They recorded epicortical brain activity in spontaneously behaving rats, allowing them to investigate associations between patterns of neural activity and behavioral events.