Synthesis-identification integration: One-pot hydrothermal preparation of fluorescent nitrogen-doped carbon nanodots for differentiating nucleobases with the aid of multivariate chemometrics analysis

Ultrasensitive detection of microRNA-21 by using specific interaction of antimonene with RNA as electrochemical biosensor

MicroRNA exhibits different levels of expression in cancer and can affect the transformation, metastasis, and carcinogenesis of the cancer cell. Herein, we developed a novel kind of electrochemical microRNA biosensor based on two-dimensional nanomaterial of antimonene nano-flakes (AMNFs) and carbon quantum dots (CQDs) which were used as substrating to cadmium ion (Cd²⁺) for specific detection of breast cancer-relevant biomarker-microRNA-21. Compared to graphene, the first principle energetic calculation shows that the AMNFs have completely a stronger force interaction with single strand (ssRNA), due to the antimonene has a more delocalized 5 s/5p orbital. After the addition of complementary microRNA, due to the low adsorption affinity of double-stranded RNA (dsRNA) to antimonene, the hybridized target is easy to desorb from the antimonene interface, and the oxidation peak of metal ions is significantly reduced. Results showed the microRNA-21 concentration can be detected from 100 aM to 1 nM, the limit of detection as low as 21 aM toward microRNA-21, which is 3 times lower than those of the established microRNA biosensors. The unique combination of not be attempted before existing sensing material which has special adsorption properties represents an approach to the detection of breast cancer. And it provides a promising method for early diagnosis, monitoring, and staging of breast cancer.

Fluorescent Carbon Dots Prepared from Hazelnut Kohl as an Affordable Probe for Determination of Dopamine

In this investigation, a simple, green and facile fluorescence mrtod using carbon dots (CDs) of hazelnut kohl is described for selective detection of dopamine (DA). The sensing system is based on hazelnut kohl (the black soot of kohl) which is used as a carbon source. Generally, kohl is a traditional eye cosmetic that used in different parts of the world and synthesized by the combustion process like burning natural materials. Here, it has been proven that black soot (kohl) obtained from hazelnut has a carbon dot structure and can be used for sensory applications. Some characterization methods are carried out to reveal the kohl structure. Also, the photoluminescence properties of the prepared CDs of kohl are investigated. It is found that the size of CDs is 2-4 nm. Besides, under the optimal conditions, the fluorescence of CDs is used for DA determination. CDs fluorescence intensity is decreased linearly with the increase of DA concentration. By using the fluorescence dependency toward the DA concentration, DA can be determined in the range 0.5-30 μM with the limit of detection of 0.30 μM. Finally, this method is successfully applied to discriminate the DA in the real samples (healthy human serum and cerebrospinal fluid (CSF)) which shows acceptable efficiently for diagnostic purposes. The fluorescence of carbon dots, prepared from Hazelnut Kohl, is quenched in the presence of dopamine.

Adenine-stabilized carbon dots for highly sensitive and selective sensing of copper(II) ions and cell imaging

Adenine-stabilized carbon dots (A-CDs) are shown to be a viable fluorescent probe for highly sensitive detection and imaging of Cu²⁺. The probe has a linear fluorometric response in the 1-700 nM concentration range and a 0.3 nM detection limit. The probe, with excitation/emission maxima at 380/435 nm, is highly selective for Cu²⁺ over other metal ions, anions, amino acids, and biomolecules. The fluorescence quenching mechanism of the A-CDs by Cu²⁺ is investigated using transmission electron microscopy images coupled with elemental mapping, X-ray photoelectron spectroscopy, X-ray-excited Auger electron spectroscopy, fluorescence lifetime, UV-visible spectroscopy, and cyclic voltammetry. The experimental results show that the fluorescence quenching is caused by the combination of Cu²⁺-coordination-induced aggregation of the A-CDs, the reduction of Cu²⁺ by the A-CDs, and the nonradiative photoinduced electron transfer process from the A-CDs to Cu²⁺ or metallic Cu. The high sensitivity and high selectivity of the sensor are ascribed to the chemical interactions between the A-CDs and Cu²⁺, the photophysical process between the A-CDs and Cu²⁺, and the high fluorescence quantum yield of the A-CDs (44.6%). The A-CDs have excellent water solubility, good stability to variation of pH values, high photostability, fast response time, and low cytotoxicity. They are successfully employed for intracellular imaging of Cu²⁺ in HepG2 cells and Cu²⁺ detection in the tap water samples.

Evolution and Synthesis of Carbon Dots: From Carbon Dots to Carbonized Polymer Dots

Despite the various synthesis methods to obtain carbon dots (CDs), the bottom-up methods are still the most widely administrated route to afford large-scale and low-cost synthesis. However, as CDs are developed with increasing reports involved in producing many CDs, the structure and property features have changed enormously compared with the first generation of CDs, raising classification concerns. To this end, a new classification of CDs, named carbonized polymer dots (CPDs), is summarized according to the analysis of structure and property features. Here, CPDs are revealed as an emerging class of CDs with distinctive polymer/carbon hybrid structures and properties. Furthermore, deep insights into the effects of synthesis on the structure/property features of CDs are provided. Herein, the synthesis methods of CDs are also summarized in detail, and the effects of synthesis conditions of the bottom-up methods in terms of the structures and properties of CPDs are discussed and analyzed comprehensively. Insights into formation process and nucleation mechanism of CPDs are also offered. Finally, a perspective of the future development of CDs is proposed with critical insights into facilitating their potential in various application fields.

Facile Conversion of Toxic Cigarette Butts to N,S-Codoped Carbon Dots and Their Application in Fluorescent Film, Security Ink, Bioimaging, Sensing and Logic Gate Operation

The present work is emphasized on converting toxic cigarette butts (CBs) into highly fluorescent N,S-codoped carbon dots by a facile hydrothermal approach and exploring their multiple applications. The as-produced carbon dots (CBCDs) exhibited bright and stable fluorescence with a quantum yield of 26% and used as a label-free probe for "on-off-on" sequential detection of Fe3+ and ascorbic acid (AA). The fluorescence of CBCDs can be significantly quenched by Fe3+ ions through static quenching and restored upon the subsequent addition of AA due to the reduction of Fe3+ to Fe2+ by AA. This nanoprobe presented great selectivity and excellent sensitivity to Fe3+ and AA with a detection limit of 0.13 and 0.2 μM, respectively. Furthermore, the nanoprobe was extended to biosystem (intracellular detection) and successfully applied for the detection of Fe3+ in real water (tap, bore, and pond) and AA in biological samples (human urine and serum). In addition, we have constructed an IMPLICATION logic gate based on these unique sensing characteristics. The "visible-invisible" and "UV-visible" property explored their use as invisible ink for security applications. Furthermore, highly photostable fluorescent polymer films were prepared by incorporating CBCDs in poly(vinyl alcohol). It is anticipated that the strong and stable fluorescence emission nature of these films might find direct or indirect applications in various optical/optoelectronic devices, ranging from fluorescent displays to light-emitting diodes.