Citrate‐Based Fluorescent Biomaterials

Abstract

Fluorescence imaging has emerged as a promising technique for monitoring and assessing various biologically relevant species in cells and organisms, driving the demand for effective fluorescent agents with good biocompatibility and high fluorescence performance. However, traditional fluorescent agents, such as quantum dots (QDs) and organic dyes, either suffer from toxicity concerns or poor fluorescence performance (e.g., low photobleaching-resistance). In this regard, citrate-based fluorescent biomaterials, which are synthesized from the natural and biocompatible precursor of citric acid (CA), have become competitive alternatives for fluorescence imaging owing to their biocompatibility, cost effectiveness, straightforward synthetic routes, flexible designability, as well as strong fluorescence with adjustable excitation/emission wavelengths. Accordingly, numerous citrate-based biomaterials, including carbon dots (CDs), biodegradable photoluminescent polymers (BPLPs), and small molecular fluorophores, have been developed and researched in the past few decades. This review discusses recent progress in the research and development of citrate-based fluorescent materials with emphasis on their design and synthesis considerations, material properties, fluorescence properties and mechanisms, as well as biomedical applications. It is expected that this review will provide an insightful discussion on the citrate-based fluorescent biomaterials, and lead to innovations for the next generation of fluorescent biomaterials and fluorescence-based biomedical technology.

Carbon Dots from Citric Acid and its Intermediates Formed by Thermal Decomposition

“…The presence of this band, not observed in the precursor (Figure ), indicates the formation of an intermediate species during the dehydration of CAM. This intermediate is itaconic acid, as determined by comparing all the possible compounds and their FTIR signatures in this infrared region (Scheme and Figure S1 in the Supporting Information).…”

“…CA C‐dots and citrate‐based fluorescent materials have, however, intrinsic advantages, namely low toxicity and good biocompatibility. They have been, therefore, widely applied for developing fluorophores for biomedical applications …”

“…They have been, therefore, widely appliedf or developing fluorophores for biomedical applications. [8][9][10][11] One of the simplest routes to synthesise fluorescent C-dots from citric acid is thermal decomposition;d uring the treatment,C Ai sd ehydrated and reducedi nt he 180-200 8Ct emperaturer ange to obtain af luorescent material. The preparation of C-dotsf rom CA is, however,v ery sensitive to the synthesis conditions, such as decomposition temperature, time of thermal treatment [12] and use of solvent.…”

Carbon Dots Induce Epithelial‐Mesenchymal Transition for Promoting Cutaneous Wound Healing via Activation of TGF‐β/p38/Snail Pathway

“…[10] Carbon dots (CDots) are less than 10 nm carbonbased nano particles with several distinct merits, such as low cytotoxicity, abundant raw material, easy preparation, and fluorescence properties, thus showing great potential in various biomedical applications, including antiinflammation, [29] bacteriostasis, [30] bioimaging [31] and so on. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Meaningfully, through neutral izing the reactive oxygen species from inflammation/infec tion and sterilizing the bacteria in the wounds, CDots could be utilized to accelerate wound healing. [48,49] Despite these achievements, however, only the contaminated and dirty infected wounds usually need antibacterial treatment, [50] but a rapid reepithelialization of the wound surface for forming the epidermal barrier is significant in various wounds.…”

Carbon Dots Derived from the Maillard Reaction for pH Sensors and Cr (VI) Detection

“…pH is a crucial target parameter in the industrial, biomedical and environmental applications [ 20 ]. Traditional small molecule pH probes usually suffer from relatively narrow and weak absorption spectra, toxicity concerns, poor emission performance and low photobleaching resistance [ 21 ]. The CDs as novel fluorescent nanomaterial has unique properties, especially low toxicity and biocompatibility.…”