New Opportunities: Second Harmonic Generation of Boron‐Doped Graphene Quantum Dots for Stem Cells Imaging and Ultraprecise Tracking in Wound Healing

Abstract

Second harmonic generation (SHG) has recently emerged, having the advantages of no bleaching, no blinking, and no signal saturation, as well as a high signal to‐noise ratio compared to fluorescence. Existing SHG probes are based on heavy metal or organic dye molecules, which have the shortcomings of toxicity, a large size, or photoinstability. To address the urgent need for long‐term tracking and imaging in organisms, boron‐doped graphene quantum dots (B‐GQDs), a highly biocompatible graphene based with a strong and photostable SHG signal is first synthesized and is further applied for stem cell imaging and tracking in wounds. The results demonstrate the possibility of stem cell internalization of B‐GQDs as a SHG probe and show no hindering of the stem cell's central physiological activities such as differentiation. Most importantly, B‐GQDs are successfully tracked in skin tissue in vivo after the labeled mouse mesenchymal stem cells being implanted over 35 days. This work will inspire the development of doped graphene quantum dot materials and promote the broad use of B‐GQDs in future molecular imaging, drug delivery, and stem cell therapy.

Tuning the Surface Chemistry of Second-Harmonic-Active Lithium Niobate Nanoprobes Using a Silanol–Alcohol Condensation Reaction

“…60−62 These properties enable SHG probes to be used in the study of thick samples, such as deep-tissue imaging. 2,[52][53][54]56,57 The SHG nanoprobes also enable long-term (e.g., months) monitoring and tracking of biological processes in whole organisms and tissues. 2,[52][53][54]56,57 Although SHG probes based on LiNbO 3 NPs have several advantages over fluorescent molecules, further development of SHG probes for bioimaging will require methods to tune their surface chemistry.…”

“…2,[52][53][54]56,57 The SHG nanoprobes also enable long-term (e.g., months) monitoring and tracking of biological processes in whole organisms and tissues. 2,[52][53][54]56,57 Although SHG probes based on LiNbO 3 NPs have several advantages over fluorescent molecules, further development of SHG probes for bioimaging will require methods to tune their surface chemistry. For example, functionalizing the surfaces of these nanoprobes with biologically relevant molecules will be essential to improve their colloidal stability and to enable multimodal tracking and validation of their location within biological systems.…”

Plasmonic Optical Tweezers for Particle Manipulation: Principles, Methods, and Applications

“…Second-harmonic imaging is a label-free technique that is based on a nonlinear optical effect named second-harmonic generation (SHG). SHG does not need the excitation of molecules to provide fluorescence, which means it does not suffer from the side effect of phototoxicity and photobleaching. , Hence, it becomes a promising alternative imaging technique. Recently, the idea of further enhancement of SHG utilizing the tightly confined electromagnetic field induced by plasmonic nanostructures has attracted more and more attention. − By integration with POT, the performance of second harmonic imaging can be further improved with the target strictly confined in the hotspot of the plasmonic nanostructures.…”

“…SHG does not need the excitation of molecules to provide fluorescence, which means it does not suffer from the side effect of phototoxicity and photobleaching. 217,218 Hence, it becomes a promising alternative imaging technique. Recently, the idea of further enhancement of SHG utilizing the tightly confined electromagnetic field induced by plasmonic nanostructures has attracted more and more attention.…”

Boronate affinity material-based sensors for recognition and detection of glycoproteins

“…However, at present, there is not much research on the use of BAMs for glycoprotein recognition and imaging of living biological cells. In contrast, a large number of fluorescent BAMs have been proposed for cell imaging to recognize cell membrane glycans, usually using QDs, 120,121 traditional fluorescent dye, 122,123 and conjugated polymers 124,125 as fluorescence donors. QDs are characterized by controllable size emission wavelength, great photostability, broad excitation and narrow emission, compared with traditional fluorescent dyes.…”