Surface functional groups strongly affect the properties of carbon dots (CDs). Amino, carboxy, and hydroxy groups are most commonly encountered in CDs, and they can be introduced via covalent and noncovalent modification. This article (with 116 refs.) reviews the progress made in the past few years. Following an introduction into the field, a large section covers methods for covalent modification (via amide coupling reactions, silylation, and other reactions including esterification, sulfonylation and copolymerization). Next section reviews methods for noncovalent modifications (π interactions, complexation/chelation, and electrostatic interactions). The resulting modified CDs are powerful nanomaterials for targeting and extracting analytes, and in drug release. The modification of the surface also affects fluorescence quantum yields, complexation capacity, the color of fluorescence, and their quenching capability. Current challenges are critically assessed in the concluding section.

Surface modification and chemical functionalization of carbon dots: a review

Quantum dots are semiconductor nanocrystals that inherently fluoresce at specific wavelengths in the visible, enabling a number of potential applications to be realized. However, conventional quantum dots are based on metallic elements, which has raised concerns over toxicity, stability and high cost. As a result, the search for more benign substitutes is a worthwhile yet challenging undertaking. Recently a new type of visible emitters has been reported exclusively based on functionalized carbon nanoparticles. The carbon dots were 5 nm in diameter and were produced via laser ablation of graphite. Surface oxidation with nitric acid and subsequent covalent grafting of organic moieties afforded light-emitting derivatives. Notably, the light emitted by these dots depends on the wavelength of light used for excitation. It was suggested that the tethered modifier stabilizes the surface of the carbon nanoparticles helping to generate energy traps that emit light when stimulated, an effect described as emission from passivated surfaces. Because of its origin the emission is size-dependent, i.e., the smaller the size of the dots the better their photoluminescence efficiency. In another intriguing approach, photoluminescent carbon dots 3 nm in size were directly fabricated by electrochemical shocking of multi-wall carbon nanotubes. The demonstrated photoluminescence adds another dimension to the versatility of carbon-based

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-005201.pdf

Surface Functionalized Carbogenic Quantum Dots

Significant improvements in disease management have been achieved in the past few decades. Using cancer as an example, survival rates have increased dramatically in economically developed countries, according to the World Cancer Report published by WHO in 2014.1 One of the highlights is the average 5-year survival rate of children diagnosed before the age of 15 years in Britain increased from less than 30% in 1966-70 to almost 80% in 1996-2000. The improvement can be attributed to the establishment of early screening and awareness programs, identification of a large number of genetic or non-genetic risk factors or markers, and availability of diverse therapeutic strategies including surgery and treatments using radioactive reagents, small molecules, or biological drugs. Still, cancer remains one of the major causes of deaths worldwide, affecting millions of people. Survival rates in developing countries are poor, and the global and regional burden of cancer in terms of both incidence and mortality keep increasing along with the growing population and aging society. Further improvement heavily relies on early diagnosis, wide access to treatment options, and discovery of more effective biomarkers as well as anticancer drugs with high efficacy. Such demands are also applied to diagnosis and cure for all other diseases, calling for rapid advancements in high-throughput screening (HTS) technologies that can efficiently test a large number of targets and samples, monitor diverse enzymatic processes in situ, and effectively identify biologically active substances.2.

Recent Advances in Design of Fluorescence-Based Assays for High-Throughput Screening

A tailored molecular imprinting ratiometric fluorescent sensor based on red/blue carbon dots for ultrasensitive tetracycline detection

Nanomaterials as efficient platforms for sensing DNA.

A new carbon dot (CD)-based nanoprobe for the ratiometric fluorescence detection of DNA was constructed in this work. Thiazole orange (TO), a specific organic small molecular probe toward DNA, is covalently linked to the surface of CDs, acting as the recognition element and the fluorescence response unit. In the absence of DNA, the nanoprobe only emitted the blue fluorescence of CDs, whereas TO was almost nonfluorescent. Upon addition of DNA, a turn-on emission at 530 nm appeared and gradually enhanced along with the increasing of the target DNA, whereas the fluorescence of CDs was unchanged, which realized the ratiometric detection of the target DNA. The CD-TO nanoprobe showed good selectivity to parallel G-quadruplex (G4) and double-stranded (ds) DNA over antiparallel G4 and single-stranded DNA. Moreover, the ratiometric fluorescence nanoprobe exhibited high sensitivity for ssab (a dsDNA) and c-myc (a parallel G4) with a low detection limit of 0.90 and 3.31 nM, respectively. Additionally, the G4/hemin peroxidase activity inhibition experiment demonstrated that CD-TO bound to the G4s through the end-stacking mode.

Ming Jin

Papers

Thiazole Orange-Modified Carbon Dots for Ratiometric Fluorescence Detection of G-Quadruplex and Double-Stranded DNA.