A Fluorescence Inner-Filter Effect Based Sensing Platform for Turn-On Detection of Glutathione in Human Serum

Inner-filter effect of nitrogen-doped carbon quantum dots-MnO2 nanotubes for smartphone-integrated dual-mode sensing of glutathione and captopril

Nitrogen-doped carbon quantum dots (N-CQDs) exhibit unique fluorescence properties and are considered one of the best candidates for the development of fluorescence-based sensors for the detection of many analytes. In this work, a smartphone-assisted fluorescent sensor has been developed using N-CQDs and MnO2 nanotubes (MnO2 NTs) for the detection of glutathione (GSH) and captopril (CAP). N-CQDs were facilely synthesized via the solvothermal method, where o-phenylenediamine (o-PD) and urea were used as nitrogen precursors. Likewise, MnO2 NTs were synthesized using the hydrothermal method. Relying on the excellent fluorescence quenching ability of MnO2 NTs, a nanocomposite of N-CQDs and MnO2 NTs is prepared, wherein the fluorescence intensity of N-CQDs was effectively quenched in the presence of MnO2 NTs via the inner-filter effect (IFE). The addition of thiolated compounds (GSH and CAP) helped in the recovery of the fluorescence of N-CQDs by triggering the redox reaction and decomposing the MnO2 NTs. An investigation of fluorescence along with smartphone-based studies by evaluating the gray measurement using Image J software showed a great response towards GSH and CAP providing LODs of 4.70 μM and 5.22 μM (fluorometrically) and 5.76 μM and 2.81 μM (smartphone-based), respectively. The practical applicability of the sensing system has been verified using human blood plasma samples.

Terbium Phenanthroline Complex as a Luminescent Probe for the Detection of Anthrax Biomarker: Dipicolinic acid

Dipicolinic acid (DPA) is a prominent biomarker for Anthrax disease. Bacillus anthracis bacterial endospores is composed of DPA as the significant component, which on over inhalation can cause severe health issues. Such contagious and life-threatening pathogens can be employed as bioweapons or biothreat agents for spreading bioterrorism which is a major risk for national security and public health concerns. Hence, effective detection or a surveillance system is essential for preventing the growth of bioterrorism events. Herein, we have developed a Terbium - 1,10 Phenanthroline (Tb-Phen) based lanthanide luminescence complex with bright green fluorescence. On addition of DPA, the green fluorescence is turn-off at a linear range from 0.6 to 4.762 mM. In this effect, 5D4- 7F5 transition caused by 1,10-phenanthroline to Tb3+ at 544 nm is restricted due to energy transfer quenching and Inner Filter Effect (IFE). The developed probe shows good sensitivity towards the detection of DPA with other coexisting biomolecules and ions with a low Limit of Detection (LOD) of 5.029 µM. The practical feasibility was evaluated in paper strip assay and extended in real samples such as human serum and tap water with satisfactory recovery percentage. Thereby, probe finds promising application in sensing of anthrax spore biomarker (DPA) and biothreat agents.

Deep-Learning-Assisted Discriminative Detection of Vitamin B12 and Vitamin B9 by Fluorescent MoSe2 Quantum Dots

A facile and environmentally mindful approach for the synthesis of MoSe2 QDs was developed via the hydrothermal method from bulk MoSe2. In this, the exfoliation of MoSe2 was enhanced with the aid of an intercalation agent (KOH), which could reduce the exfoliation time and increase the exfoliation efficiency to form MoSe2 QDs. We found that MoSe2 QDs display blue emission that is suitable for different applications. This fluorescence property of MoSe2 QDs was harnessed to fabricate a dual-modal sensor for the detection of both vitamin B12 (VB12) and vitamin B9 (VB9), employing fluorescence quenching. We performed a detailed study on the fluorescence quenching mechanism of both analytes. The predominant quenching mechanism for VB12 is via Förster resonance energy transfer. In contrast, the recognition of VB9 primarily relies on the inner filter effect. We applied an emerging and captivating approach to pattern recognition, the deep-learning method, which enables machines to "learn" patterns through training, eliminating the need for explicit programming of recognition methods. This attribute endows deep-learning with immense potential in the realm of sensing data analysis. Here, analyzing the array-based sensing data, the deep-learning technique, "convolution neural networks", has achieved 93% accuracy in determining the contribution of VB12 and VB9.

Chlorine-doped MoS2 quantum dots embedded in a molecularly imprinted polymer for highly selective and sensitive optosensing of quercetin

Chlorine-doped MoS2 quantum dots (Cl-MoS2 QDs) embedded in a SiO2 molecularly imprinted polymer (Cl-MoS2 QDs@SiO2@MIP) have been successfully synthesized and can be used for highly selective and sensitive optosensing of quercetin. The novel environmentally friendly sensor integrated the advantages of the Cl-MoS2 QDs and MIP, high sensitivity and specific recognition for quercetin. The as-fabricated sensor is used to detect trace amounts of quercetin, and its fluorescence intensity showed a good linear decline with the increasing concentration of quercetin from 2 ng mL-1 to 200 ng mL-1 with a detection limit of 1.2 ng mL-1 (S/N = 3). The Cl-MoS2 QDs@SiO2@MIP probe was employed to assay the content of quercetin of real onion extract with good performance, which is in fine agreement with the result obtained by high performance liquid chromatography. The developed Cl-MoS2 QDs@SiO2@MIP sensor exhibits promising potential in the detection of quercetin.

A simple and convenient dry-state SEIRS method for glutathione detection based on citrate functionalized silver nanoparticles in human biological fluids

Graphical representation for determination of glutathione using citrate functionalized AgNPs enriched dry-state SEIRS method.