a fluorescent nanosensor based on carbon dots (Cdots) and
different-size MnO2 nanospheres has been synthesized for
rapid detection of glutathione (GSH). Water-soluble and highly fluorescent
Cdots were prepared by the microwave method using ascorbic acid as
the precursor. MnO2 nanospheres of different sizes (large,
medium, and small) were prepared by varying the concentration ratio
of methionine and KMnO4 at room temperature, which was
confirmed by HRTEM analysis. The different sizes of MnO2 nanospheres in Cdots result in quenching of the fluorescence intensity,
quantum yields, and average lifetime values, which suggest that the
fluorescence resonance energy transfer mechanism occurs between the
Cdots and MnO2 nanospheres. The variations of all the photophysical
parameters and fluorescence turn off properties of Cdots are significantly
tuned depending on the size of the nanospheres. Moreover, detection
of GSH in the presence of different-size Cdots@MnO2 systems
has been explored. GSH causes the redox reaction in the presence of
MnO2, which leads to transformation from MnO2 to Mn2+. As a result, fluorescence restoration (turn
on) of Cdots was observed. The large MnO2 nanospheres showed
the lowest detection limit of 15 μM for GSH. The synthesized
sensing system was very fast, simple, economical, and environmentally-friendly
for the detection of the GSH level.
In recent years, a variety of biosensors based on manganese dioxide (MnO 2 ) nanostructures were used for the detection of different biomolecules. Structural versatility and different oxidation states of Mn present in MnO 2 nanostructures significantly enhance their biosensing applications. In this review, we have mainly focused on different morphologies of MnO 2 nanostructures and their role in different types of biosensors. We are elaborately discussing the electrochemical and optical-based biosensors on different morphologies of MnO 2 and their sensing techniques with proposed mechanisms. In electrochemical biosensors, various electrodes are available but there is a need for cheap, flexible, portable, and nontoxic electrodes. Therefore, we have discussed the fabrication of MnO 2 nanostructures on the surfaces of different types of electrodes and their real-time applications. MnO 2 nanomaterials are used in various optical biosensors due to their excellent light absorption properties, and they act as strong quenching agents. MnO 2 nanomaterials are termed "alternative natural enzymes" due to their significant enzyme-like activity. The study of various morphology-dependent sensing properties of MnO 2 nanostructures provides an insight into the development of many electrochemical and optical biosensors. Recently, MnO 2 based biosensors have earned great popularity as an alternative method for fast and easy detection of many biomolecules with very low detection limits.
Heteroatom doping of graphene quantum dots (GQDs) leads to modify their intrinsic properties and used as a fluorescent sensor for the metal ions sensing. Here, Nitrogen-doped GQDs (N-GQDs) was synthesized...
Herein, we develop a facile, sensitive, and selective fluorescent nanosensor for the detection of glutathione (GSH). In this protocol, carbon dots (Cdots) with a fairly high quantum yield were synthesized by a microwave-assisted pyrolysis technique. Moreover, different shapes of the MnO 2 nanostructure were also prepared by the hydrothermal technique. A comparative photophysical study of different morphology-dependent Cdots@MnO 2 nanostructure-based biosensors was explored, which showed different results for the quenching values of ("turn-off") fluorescence intensity, quantum yields, electron transfer rate, and average lifetime. The structure, property, and performance of nanomaterials are interdependent. Therefore, the different shapes of MnO 2 , that is, nanoflowers (NFs), nanorods (NRs), and a mixture of NFs/NRs was prepared by the hydrothermal method owing to different specific surface areas (23−69 m 2 g −1 ) which put the impact on their sensing activity. It was observed that the variation in the different photophysical parameters of fluorescent Cdots such as quantum yield (Φ), average lifetime values [τ av (ns)], radiative (k r ) rate constant, nonradiative (k nr ) rate constant, rate of electron transfer (k ET ), the efficiency of electron transfer (Φ EET ), FRET efficiency (E), and Forster distance (R 0 ) were dependent on the different shapes of the MnO 2 nanostructure. These results indicate that the transfer of energy occurs between the Cdots and different shapes of MnO 2 nanostructures based on fluorescence resonance energy transfer at different charge-transfer rates. The recovery rate ("turn-on") of fluorescence of Cdots with the addition of GSH was obtained best for the NF structure by conversion of MnO 2 to Mn 2+ , and the limit of detection was obtained as ∼19 μM for GSH. The developed sensing probes were rapid, easy, cheap, and eco-friendly for the determination of GSH.
Structural versatility of MnO 2 nanostructures plays a significant role in biosensing applications. So, we have prepared simple and selective "turn-off−on" sensing probes for the detection of glutathione (GSH), based on nitrogen, sulfur codoped carbon dots (N, S-Cdots) and different morphologies of one-dimensional (1-D) MnO 2 nanostructures. N, S-Cdots with a high fluorescence quantum yield (73.42%) were prepared by a green approach through hightemperature pyrolysis in just 5 min. The different morphologies of 1-D MnO 2 nanostructures (nanowires with varying aspect ratios and nanorods) were synthesized through a hydrothermal method by varying the reaction period (8, 10, and 12 h). MnO 2 nanowires prepared at 8 h showed a high specific surface area (34 m 2 g −1 ) with a large aspect ratio. They showed significant fluorescence quenching, Stern−Volmer constants, and binding constants in the presence of N, S-Cdots. Further, ultraviolet−visible absorption, zeta potential, and time decay studies showed that the quenching mechanism of the developed sensing system was the inner filter effect, which was further confirmed by using the Parker equation. The N, S-Cdots-MnO 2 nanowire (with a high aspect ratio) sensing system showed the best limit of detection, i.e., 28.5 μM for GSH. This fast, simple, eco-friendly, and costeffective sensing system can be further used for real-time biosensing and bioimaging application.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.