Hybrid supraparticles of carbon dots/porphyrin for multifunctional tongue-mimic sensors

Carbon Dots in Enantioselective Sensing

Chirality has a crucial effect on clinical, chemical and biological research since most bioactive compounds are chiral in the natural world. It is thus important to evaluate the enantiomeric ratio (or the enantiopurity) of the selected chiral analytes. To this purpose, fluorescence and electrochemical sensors, in which a chiral modifier is present, are reported in the literature. In this review, fluorescence and electrochemical sensors for enantiorecognition, in which chiral carbon dots (CDs) are used, are reported. Chiral CDs are a novel zero-dimensional carbon-based nanomaterial with a graphitic or amorphous carbon core and a chiral surface. They are nanoparticles with a high surface-to-volume ratio and good conductivity. Moreover, they have the advantages of good biocompatibility, multi-color emission, good conductivity and easy surface functionalization. Their exploitation in enantioselective sensing is the object of this review, in which several examples of fluorescent and electrochemical sensors, containing chiral CDs, are analyzed and discussed. A brief introduction to the most common synthetic procedures of chiral CDs is also reported, evidencing strengths and weaknesses. Finally, consideration concerning the potential challenges and future opportunities for the application of chiral CDs to the enantioselective sensing world are outlined.

Room temperature cost-effective synthesis of carbon quantum dots for fluorescence pattern recognition of metal ions

Herein, a type of low-consuming carbon quantum dot (CD) has been synthesized at room temperature in just 45 minutes via Schiff base reaction between o-phthalaldehyde (OPA) and polyethyleneimine (PEI). These CDs are pH-dependent, so a novel label-free florescent sensor array can be constructed by utilizing buffers with various pH levels, which leads to distinctive fluorescence response patterns upon being challenged with metal ions for their pattern recognition. The results demonstrate that large-scale detection of metal ions can be achieved with as little as 3 types of sensors. Additionally, the sensors are able to discriminate between various metal ion concentrations and mixtures of different metal ions. The technique demonstrates potential uses in water quality monitoring by promising straightforward, quick, sensitive, and potent discrimination of metal ions.

A promising tool for clinical diagnostics: Dual-emissive carbonized polymer dots based cross-linking enhanced emission for sensitive detection of alkaline phosphatase and butyrylcholinesterase

Compared with single signal readout, dual-signal readout commendably corrects the impact of systematic or background error, achieving more accurate results for the diagnosis of many diseases. This work aimed to design and prepare dual-emissive fluorescent probes for the construction of ratiometric fluorescence biosensors to detect liver disease biomarkers. Sodium alginate (SA) with numerous potential sub-fluorophores and active sites and 4,4',4'',4'''-(porphine-5,10,15,20-tetrayl) tetrakis (benzoic acid) (TCPP) with macrocyclic conjugated structures were introduced to prepare the carbonized polymer dots (CPDs) with red/blue dual emission based on the cross-linking enhanced emission (CEE) effect and the luminescence of macrocyclic conjugated structures. The ratiometric fluorescence sensing systems were constructed by integrating the specific response of CPDs to Cu2+ and the affinity difference of Cu2+ to substrates or products of enzymes. The sensing systems, CPDs/Cu2+/PPi and CPDs/Cu2+/BTCh, were designed to detect liver disease biomarkers, alkaline phosphatase (ALP) and butyrylcholinesterase (BChE), respectively. The limit of detection for ALP and BChE was 0.35 U/L and 0.19 U/L, respectively. The proposed sensors were successfully applied to human serum samples from different health stages with satisfactory recoveries. These results demonstrate the successful design of a novel dual-emissive fluorescent probe and provide a feasible strategy for clinical detection.

Positively Charged Carbon Dots with Antibacterial and Antioxidant Dual Activities for Promoting Infected Wound Healing

Bacterial infection and excess reactive oxygen species are key factors that lead to slow or substantially delayed wound healing. It is crucial to design and develop new nanomaterials with antibacterial and antioxidative capabilities for wound healing. Here, positively charged carbon dots (CDs) are rationally designed and synthesized from p-phenylenediamine and polyethyleneimine by a facile one-pot solvothermal method, which show good biocompatibility in in vitro cytotoxicity, hemolysis assays, and in vivo toxicity evaluation. The positively charged CDs show superior antimicrobial effect against Staphylococcus aureus (S. aureus) at very low concentrations, reducing the risk of wound infection. At the same time, CDs with surface defects and unpaired electrons can effectively scavenge excess free radicals to reduce oxidative stress damage, accelerate wound inflammation-proliferation transition, and promote wound healing. The mouse model of skin infection demonstrates that CDs can effectively promote the wound healing of skin infection without obvious side effects by simply dropping or spraying onto the wound. We believe that the prepared CDs have satisfactory biocompatibility, antioxidant capacity, and excellent antibacterial activity and have great application potential in wound healing.

A facile way to construct sensor array library via supramolecular chemistry for discriminating complex systems

Differential sensing, which discriminates analytes via pattern recognition by sensor arrays, plays an important role in our understanding of many chemical and biological systems. However, it remains challenging to develop new methods to build a sensor unit library without incurring a high workload of synthesis. Herein, we propose a supramolecular approach to construct a sensor unit library by taking full advantage of recognition and assembly. Ten sensor arrays are developed by replacing the building block combinations, adjusting the ratio between system components, and changing the environment. Using proteins as model analytes, we examine the discriminative abilities of these supramolecular sensor arrays. Then the practical applicability for discriminating complex analytes is further demonstrated using honey as an example. This sensor array construction strategy is simple, tunable, and capable of developing many sensor units with as few syntheses as possible.

A fluorescent sensor array based on three kinds of carbon dots for identification of hydroxybenzaldehyde and nitrobenzaldehyde isomers

A fluorescent sensor array based on three kinds of different CDs exhibited diverse fluorescence patterns for each hydroxybenzaldehyde and nitrobenzaldehyde isomer, which were further analyzed by principal component analysis (PCA).

Rotating the C-N Bond in a Coumarin-Pyridine-Based Sensor for Pattern Recognition of Versatile Metal Ions

A cross-reactive sensor array is powerful for high-throughput discrimination of various kinds of metal ions. However, the construction of a multicomponent sensor array is always time-consuming and cost-ineffective. Herein, a practical four-component X1-based sensor array (X1SA) was obtained by simply dissolving a single dye molecule X1 in respective solvents such as methanol, ethanol, dimethyl sulfoxide, and acetonitrile. In this design, X1 exhibits strong solvatochromic fluorescence properties via an excited-state intramolecular proton transfer and intramolecular charge transfer combined mechanism. Moreover, rotation of the C-N bond between the pyridine and coumarin units in X1 enabled it to coordinate with metal ions through different binding modes, which acted as an additional dimension of the sensor array. Inspired by this C-N bond rotation strategy, X1SA was determined to be powerful in discriminating 20 kinds of metal ions in both phosphate-buffered saline and 5% serum media in a range of 0.1-100 μM. In addition, the sensor array was also successfully applied in differentiating similar and mixed metal ions such as Fe³⁺/Fe²⁺, Cd²⁺/Hg²⁺, and Sn²⁺/Pb²⁺ in serum samples, which is meaningful for investigating the biological roles of iron and early diagnosis of related metal poisoning accidents.