Review of 2D MnO₂ Nanosheets as FRET-Based Nanodot Fluorescence Quenchers in Chemosensing Applications

Abstract

In the past decade, a variety of MnO 2 nanostructures have been used in chemosensing applications because of their unique redox properties, structural diversity, and broad absorption band, which makes them good energy acceptors. The most common strategy in Forster (or fluorescence) resonance energy transfer (FRET)-based chemosensing assays is to use low-dimensional fluorescent dots like carbon-based dots, metal dots, and even fluorescent dyes to form donor−acceptor pairs with 2D MnO 2 nanosheets (NSs). This review is a collection of the current library on fluorescent nanodots and MnO 2 NSs-based FRET conjugates as sensing platforms with a focus on highlighting the strategies involved in the detection of various analytes. Commonly, an analyte-triggered redox reaction results in the decomposition of MnO 2 NSs, leading to the release of fluorescent nanodots in solution for the turn-on detection of various reducing species. We intend to elaborately discuss the systematic upgradation of detection strategies involving fluorescent dots@2D MnO 2 NSs. Recently, a cascade of redox reactions was judiciously employed to target several bioanalytes involving a fluorescent dots@MnO 2 NSs FRET conjugate in a selective and sensitive manner. These sensing assays are categorized by the use of different fluorescent nanodots [carbon dots (CDs) and graphene quantum dots (GQDs), polymer dots, metal dots, etc.] with 2D MnO 2 NSs as FRET pairs in different sensing applications. Further, the analytes were categorized as reducing species, oxidants, enzymes, microbes, etc. The focus was paid to the sensing efficiency of the analytical tool. As a part of the study, a brief account of the synthesis of nanodots and MnO 2 NSs, their properties, and the FRET mechanism is also included. In a few cases, the sensing mechanism follows an inner filter effect without a prerequisite of the distance between the fluorophore and quencher units in the sensing of analytes, which are also covered in this collection. The available literature indicates a bright future for these FRET-based contemporary sensing strategies as environmentally benign, cost-effective, label-free techniques, which are discussed in the end.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

“…Therefore, MnO 2 NSs have been used as auxiliary NPs to detect reducing substances, such as AA and GSH, using FNPs such as CDs, QDs, and even fluorescent dyes to form donor-acceptor pairs. 295 Based on the fluorescence quenching ability of MnO 2 NSs, many DRPFs have been designed. [296][297][298][299] Chen's group designed an Au/Ag NCs-MnO 2 -VB1 (VB1 stands for thiamine) ternary system for the detection of proanthocyanidins.…”

Overview on the Development of Alkaline-Phosphatase-Linked Optical Immunoassays

“…For example, V 2 O 5 nanobelts, cobalt oxyhydroxide (CoOOH), and MnO 2 NSs with a broad and intense adsorption spectrum can serve as efficient nanoquenchers to almost completely quench the fluorescence of different nanomaterials, such as CDs, upconversion nanoparticles (UCNPs), polydopamine, and GQDs [ 99 , 100 , 101 , 102 ]. The generated AA serving as a reducing agent can react with these nanomaterials to release metal ions and restore the fluorescence [ 103 , 104 , 105 , 106 , 107 ]. Li et al developed a fluorescence immunoassay for imidacloprid detection by degrading the structure of CoOOH NSs by ALP-enzymatic products ( Figure 10 A) [ 108 ].…”

In Situ Cancer-Cell-Triggered Visible Changes in Mechanical Properties, Electroconductivity, and Adhesiveness of a MnO2@PD-Based Mineralized Hydrogel

“…Additionally, MnO 2 's exceptional light absorption acts as a potent quencher in FRET-based conjugates, facilitating the development of "turn off−on" FL sensing probes. 19,20 In this study, we designed an ROS-and GSH-responsive dopamine-conjugated hyaluronic acid carbonized sp 2 -rich PDencapsulated mineralized hydrogel (M@PD) that provides cancer-cell-triggered visible mechanical change as well as a fluorescence-and electrochemical-based approach for cancer diagnosis. The increased levels of GSH and H 2 O 2 in cancer cells relative to normal cells serve as biomarkers for cancer detection.…”

“…In cancer sensing, the breakdown of MnO 2 into Mn 2+ by GSH and ROS enables tunable conductivity. Additionally, MnO 2 ’s exceptional light absorption acts as a potent quencher in FRET-based conjugates, facilitating the development of “turn off–on” FL sensing probes. , …”