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The development of bimodal systems with signals for two diagnostic techniques has been increasing. Magnetic resonance imaging (MRI) is a non-invasive technique that distinguishes pathological tissues from healthy ones. To improve the images' contrast, nanoparticulate contrast agents (CAs) have been developed, allowing for the attachment of several CA molecules in one nanoparticle. In this work, we associated AgInSe2 quantum dots (QDs) with gadolinium complexes, obtaining nanoprobes for MRI and optical imaging. The nanosystems showed good optical properties and values of relaxivity superior to the CAs used clinically. Thus, these nanoprobes have the potential to be used as CAs for MRI and optical imaging. [ABSTRACT FROM AUTHOR]

In this paper, we proposed an efficient method for mercury(II) and glutathione detection using a fluorescent nanoprobe as a sensor. Carbon dots were synthesized from polyethyleneimine and ammonium citrate via a one-step hydrothermal method. The fluorescence of carbon dots was quenched since electron transfer occurred due to the interaction between mercury(II) and functional groups on the surface of carbon dots. Adding glutathione to the carbon dots-mercury(II) system, the fluorescence was recovered due to the stronger binding ability of glutathione to mercury(II). Based on the above-mentioned principle, this "off-on" fluorescent sensor can easily achieve the detection of mercury(II) and glutathione, which provided limits of detection of 22.45 nM and 61.89 nM, respectively. In this paper, the proposed method has been applied to detect mercury(II) and glutathione in real lake water and serum, respectively, and a logic gate for sensing glutathione was presented. The developed "off-on" fluorescent sensor with high sensitivity and selectivity has shown great potential for mercury(II) and glutathione detection in environmental and biosensing fields. [ABSTRACT FROM AUTHOR]

Ratiometric fluorescence (FL) probes can eliminate the background interference and provide more accurate detection results than single emission intensity-based nanoprobes. Recently, carbon dots (CDs)-based ratiometric FL probes have received extensive research attention due to their excellent biocompatibility, water solubility, and multi-emission capabilities. In this review, we firstly summarize the construction strategies of CDs-based ratiometric FL probes, including physical mixing, nanohybrid, and dual-emitting CDs strategies. Additionally, we classify the sensing types of CDs-based ratiometric FL probes into five categories according to the difference in spectral variation caused by analytes: "single-response-ON", "single-response-OFF", "double-responses-ON", "double-responses-OFF", and "double-responses-Reverse" types. Finally, a thorough overview of CDs-based ratiometric FL probe applications in ions, molecules, pH, and temperature sensing is provided. We believe this review can show the latest research progress of CDs-based ratiometric FL sensing fields and provide perspectives on future developments for the construction of CDs-based ratiometric FL probes and their potential applications. [ABSTRACT FROM AUTHOR]

Excitation-emission orthogonalized luminescent upconversion nanoparticles (OUCNPs), which can respond to changes in external stimuli accordingly, show great promise in many intelligent applications. However, the construction of such materials mostly relies on the selective absorption of Nd3+ and Yb3+ at different wavelengths and the long-range energy migration between the layers, resulting in complex structures and limited orthogonal luminescence intensity. Herein, we developed a relatively simple structure of OUCNPs (β-NaErF4@NaLuF4@NaYF4:20%Yb, 2%Er@NaLuF4), where the fluorescence emission switches from red to green when the excitation wavelength is shifted from 808 to 980 nm. This structure exhibits high-quality, independent, and non-interfering orthogonal luminescence properties without Nd3+ sensitization and long-range energy migration. As a proof of concept, we demonstrate the application of the designed OUCNPs in anti-counterfeiting. We also prepared OUCNPs@PEI (PEI = polyethylenimine) self-referencing fluorescent probes to enable quantitative analysis of trinitrotoluene (TNT) in solution with a detection limit of 3.04 µM. The probes can be made into test strips for portable on-site visual detection of TNT, and can also be used to image latent fingerprints and detect explosive residues in fingerprints simultaneously. The concept proposed in this work can be extended to the visual detection of a larger range of organic and biological molecules, and is highly promising for practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fluorescent nanoprobe sensor depending on using luminescent metal organic framework (LMOF). • Fluorescent probe for a non-chromophoric food additive monosodium glutamate(MSG) • The nanoprobe was applied to determine this food additive in the instant noodles. • AGREE, AGREEprep, and BAGI metrics were evaluated for the method. This work reports the development and application of a new fluorescent nanoprobe sensor depending on using luminescent metal organic framework (LMOF). The developed sensor composed of hybridized Ca 1,3,5-benzenetricarboxylic acid metal organic framework with microcrystalline cellulose (Ca-BTC/MCC MOF) as a fluorescent probe for the determination of the monosodium glutamate (MSG), a non-chromophoric food additive. The developed sensor was characterized using a high-resolution scanning electron microscope (HR-SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The Ca-BTC/MCC MOF hybrid, examined under the HR-SEM, showed morphological features different from the MCC and the Ca-BTC MOF. The diffraction patterns of Ca-BTC/MCC composites clearly displayed the characteristic Ca-BTC MOF diffraction bands, indicating that MCC was successfully incorporated in the formation of crystalline MOF hybrids. The FTIR spectra show the bands of MCC, as well as the bands of Ca-BTC MOFs. The prepared nanoprobe was successfully applied as a sensitive sensor for the determination of MSG in food sample. The method was validated following the International ICH (Q2)R2 guidelines in terms of precision, trueness and other main analytical figures of merit, comprised the green profile and practicability metrics. A wide linearity range was achieved (5–50 µg/mL) with good correlation coefficient (R2 ≥ 0.9993). The recoveries (%) were found in the range of 100.0 to 101.5 and the RSDs (%) were in the range of 0.1 to 0.9 %. These results show that the developed nanoprobe was selective, and highly accurate to determine this important food additive in the seasonings of instant noodles, also showing a reduced environmental impact based on the metrics currently accepted for the evaluation of the green profile and practicability. [ABSTRACT FROM AUTHOR]

• Copper peroxide nanodot was utilized as signal nanoprobe for photoelectrochemical sensor. • The nanodots were encapsulated in metal-organic frameworks. • The nanoprobe can self-supply H 2 O 2 by encapsulated CPNs under acidic condition. • The produced H 2 O 2 can help generate insoluble precipitation onto sensor surface. • The formed precipitation resulted in decrease of photoelectrochemical current intensity. Signal nanoprobe based on copper peroxide nanodots (CPNs) embedded within metal–organic frameworks (ZIF-8) was applied for developing photoelectrochemical (PEC) sensor for detection of circulation tumor cells (CTC). The nanoprobe can self-supply H 2 O 2 by encapsulated CPNs under acidic condition. The produced H 2 O 2 can help generate insoluble precipitation onto sensor surface in the presence of horseradish peroxidase (HRP), leading to suppressed PEC current intensity. MCF-7 was selected as model CTC, which was enriched and separated from samples by antibody modified magnetic beads (MB). Organic semiconductor BTA-C4Ph and PM6 were chosen to form n-p heterojunction on sensor surface with enhanced PEC current intensity. The PEC sensor was constructed based on "sandwich" protocol, which has a linear range from 5 cell/mL to 100 cell/mL and a limit of detection (LOD) of 3 cell/mL (S/N = 3) for MCF-7. What more, the sensor was successfully applied for detection of MCF-7 in whole blood samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • Designed graphene quantum dots (GQDs) and MnO 2 -nanosheet-based fluorescent nanoprobe (GQDs@MnO 2 -NS). • Fluorescent GQDs@MnO 2 -NS demonstrates high sensitivity for the detection of lactoferrin. • Redox reaction between lactoferrin and MnO 2 -NS resulted in the reappearance of fluorescence emission of GQDs. • The envisioned fluorescent biosensor will present a novel complement for the diagnosis of periodontal disease. Lactoferrin estimation is increasingly acquiring prominence as a novel biomarker for the diagnosis of periodontal disease. To date, diverse lactoferrin detection methods which include electrochemical, surface-enhanced Raman scattering, colorimetric, and others have been extensively portrayed. Unfortunately, these systems have significant shortcomings including low sensitivity, selectivity, high cost, arduous and time-consuming technique, and so forth. Recently, the fluorescence-based method shows remarkable uniqueness that overcomes the demerits of traditionally reported techniques. Therefore, graphene quantum dots (GQDs) and manganese dioxide nanosheets (MnO 2 -NS) based simplistic, highly sensitive, and selective fluorescent turn 'Off-On' mediated GQDs@MnO 2 -NS nanoprobe was designed. Herein, MnO 2 -NS addition demonstrated the quenching of GQDs containing fluorescence through inner filter effects (IFE) and strong interaction between GQDs and MnO 2 -NS. The lactoferrin addition destroyed the MnO 2 -NS and fluorescence emission of GQDs reappeared which may be because of redox reaction between lactoferrin and prepared MnO 2 -NS. Herein, nanoprobe offers a wide concentration range and low limit of detection of 5 to 1600 ng/mL and 1.69 ng/mL, respectively. As fabricated GQDs@MnO 2 -NS nanoprobe sensor demonstrated high selectivity, good stability, and reproducibility towards lactoferrin that assuring applicability of biosensor. Therefore, the GQDs@MnO 2 -NS nanoprobe will offer a simplistic sensor with adequate sensitivity to achieve highly responsive and selective detection of lactoferrin. [ABSTRACT FROM AUTHOR]

UV–visible absorption spectra and probe image before and after Cys interaction. [Display omitted] • Cit Au NPs was synthesized by chemical reduction method. • Selective detection towards cysteine was observed with LOD of 0.012 nM. • Temperature and salinity did not influence Cys detection. • XPS spectra of cit-Au-Cys-Cr(III) complex was used to elucidate mechanism. • Practical applicability of Cit-Au NPs probe was tested with milk, urine, blood serum and environmental samples. A selective and sensitive detection of L-cysteine (Cys) is an important tool for various biological studies. Here, Au nanoparticles (NPs) were prepared by chemical reduction technique. The probe was developed to detect and quantify Cys in the presence of Cr3+ ions which acts as a cross linker. The citrate capped Au NPs probe was analyzed by UV–visible spectrophotometry, TEM, EDAX, FTIR, DLS, XPS and zetasize. The zeta potential and effective size of Au NPs were −41.22 mV and 12 nm, respectively. The Cys interaction with Au NPs showed drastic colour variation from red to purple and colourless with rapid response time of 1 min. The limit of detection (LOD) of Au NPs probe was as low as 0.012 nM. The TEM image of Au NPs after Cys interaction verified the aggregation that resulted in colour change. The XPS core level scans of Au 4f showed 0.3 eV red shift when Cys was interacted. The Au NPs sensor is highly selective for Cys with excellent reproducibility. Acidic pH slightly favored Cys detection. Further, the probe was applied to estimate Cys quantity from milk, urine, blood and environmental augmented samples in the presence of other amino acids. The study suggests that the proposed Au NPs could detect Cys with high accuracy from various biological samples. [ABSTRACT FROM AUTHOR]