Sanjeev K. Bhardwaj

Immunosensing of Atrazine with Antibody-Functionalized Cu-MOF Conducting Thin Films.

This work reports the assembly of thin films of a silica (SiO2)-modified copper-metal organic framework, Cu3(BTC)2 [Cu3(BTC)2@SiO2, BTC = benzene-1,3,5-tricarboxylic acid] on a conducting substrate of NH2-BDC [NH2-BDC = 2-aminobenzene-1,4-dicarboxylic acid] doped polyaniline (PANI). Assembled Cu3(BTC)2@SiO2/BDC-PANI thin films displayed electrical conductivity in the range of 35 μA. These thin films were conjugated with antiatrazine antibodies to create a novel immunosensing platform. Various structural and spectral characteristics of the synthesized material and its bioconjugate were investigated. The developed immunosensor was used for the conductometric sensing of atrazine. The detection of atrazine was achieved with a high sensor sensitivity (limit of detection = 0.01 nM) and specificity in the presence of diverse pesticides (e.g., endosulfan, parathion, paraoxon, malathion, and monochrotophos).

Bacteriophage conjugated IRMOF-3 as a novel opto-sensor for S. arlettae

This article reports the novel assembly of a bacteriophage-based fluorescent sensor for the selective and sensitive detection of a model bacterium ‘Staphylococcus arlettae (S. arlettae)’. A host specific bacteriophage was bioconjugated with a fluorescence metal organic framework ‘IRMOF-3’. Changes in the photoluminescence intensities of this fluorescent probe were correlated with bacterial concentrations. The proposed bacteriophage based opto-sensor provided a low detection limit (100 cfu mL−1) along with specificity in the detection with respect to other some non-specific bacteria, e.g. S. aureus and E. coli. The detection was achieved over a wide range of bacterial concentrations, i.e. 102–1010 cfu mL−1S. arlettae. Compared to antibody and DNA based optical sensors, the use of bacteriophage in conjugation with IRMOF-3 should offer advantages of simplicity and stability. The use of IRMOF-3 as a fluorescent molecule should also offer the development of reproducible sensors because of its well defined structural geometry and hierarchical assembly.

MOF–Bacteriophage Biosensor for Highly Sensitive and Specific Detection of Staphylococcus aureus

To produce a sensitive and specific biosensor for Staphylococcus aureus, bacteriophages have been interfaced with a water-dispersible and environmentally stable metal-organic framework (MOF), NH2-MIL-53(Fe). The conjugation of the MOF with bacteriophages has been achieved through the use of glutaraldehyde as cross-linker. Highly sensitive detection of S. aureus in both synthetic and real samples was realized by the proposed MOF-bacteriophage biosensor based on the photoluminescence quenching phenomena: limit of detection (31 CFU/mL) and range of detection (40 to 4 × 108 CFU/mL). This is the first report exploiting the use of an MOF-bacteriophage complex for the biosensing of S. aureus. The results of our study highlight that the proposed biosensor is more sensitive than most of the previous methods while exhibiting some advanced features like specificity, regenerability, extended range of linear detection, and stability for long-term storage (even at room temperature).

Formation of High-Purity Indium Oxide Nanoparticles and Their Application to Sensitive Detection of Ammonia

High-purity In2O3 nanoparticles were recovered from scrap indium tin oxide substrates in a stepwise process involving acidic leaching, liquid-liquid extraction with a phosphine oxide extractant, and combustion of the organic phase. The morphological and structural parameters of the recovered nanoparticles were investigated to support the formation of the desired products. These In2O3 nanoparticles were used for sensitive sensing of ammonia gas using a four-probe electrode device. The proposed sensor offered very quick response time (around 10 s) and highly sensitive detection of ammonia (at a detection limit of 1 ppm).

Nanomaterials for sensing of formaldehyde in air: Principles, applications, and performance evaluation

Despite the improvement in sensing technologies, detection of small and highly reactive molecules like formaldehyde remains a highly challenging area of research. Applications of nanomaterials/nanostructures and their composites have increased as effective sensing platforms (e.g., reaction time, sensitivity, and selectivity) for the detection of aqueous or gaseous formaldehyde based on diverse sensing principles. In this review, the basic aspects of important nanomaterial-based sensing systems (e.g., electrochemical, electrical, biological, and mass variation sensors) were evaluated in relation to performance, cost, and practicality of sensing gas phase formaldehyde. Accordingly, existing knowledge gaps in such applications were assessed in various respects along with suitable recommendations for building a new roadmap for the expansion of chemical sensing technology of gas phase formaldehyde.

Metal ion sensing and light activated antimicrobial activity of aloe-vera derived carbon dots

Carbon dots (CDs) have emerged out as a potential material amongst the carbon family for a wide range of applications including chemical/biological sensing, photocatalysis, bioimaging, etc. The green synthesis of these CDs from natural sources is gaining the significant interest of peer community for their wide utility. Herein, we present a facile one-step pyrolysis method for CDs synthesis from Aloe-Vera extract, which show bright blue luminescence under UV light with a quantum yield of 12.3%. Further, ex-situ morphological, structural and optical characterizations reveal their high quality and excitation independent emission behavior with the presence of carboxyl, hydroxyl functional groups. Furthermore, these CDs were studied for Fe(III) sensing in water without any surface modifications and assessed for their light activated antibacterial activity against E.Coli and Staphylococcus aureus.

An overview of different strategies to introduce conductivity in metal–organic frameworks and miscellaneous applications thereof

Metal–organic frameworks (MOFs) are known to possess many interesting material properties such as high specific surface area, tailorable porosity, adsorption/absorption capabilities, post-synthetic modifications, and chemical/thermal stabilities. Because of these unique features, they have been explored for the development of sensors for a variety of analytes. A large proportion of pre-existing MOF-based sensors are well suited for optical transductions due to a lack of electrical conduction in their pristine forms. Hence, the development of MOF-based electrochemical/electrical sensors requires specialized strategies through which MOFs are modified or hybridized with enhanced conductive moieties (e.g., via doping or post synthetic modification). In this review article, we provide a comprehensive review of various synthetic and integrating strategies to improve electrical conductivity and long-range charge transport properties in MOFs. To this end, we have compiled details of different techniques that have been used to develop electrically/electrochemically active platforms for MOF-based sensing of various targets.

Potential use of polymers and their complexes as media for storage and delivery of fragrances

ABSTRACT The use of fragrances is often essential to create an elegant, welcoming, or exhilarating environment. Through encapsulation, the release and delivery of fragrances are customized in many consumer products. For such purposes, cost‐effective techniques have been developed and employed with the use of various polymers and porous organic materials to efficiently impart fragrances to foods and various other consumer products. After entrapment or uptake/storage of fragrant molecules within a polymeric complex, the properties can be investigated by automated thermal desorption (ATD) analysis. For efficient delivery, fragrances are adsorbed (or entrapped) in some media (e.g., fabric or paper). The release of such entrapped fragrances usually is achieved by spraying. Fragrances can be also loaded in a media by purging aroma gases or by adding fragrance essence directly into a liquid medium. Porous materials, such as zeolites, have been traditionally used for air purification as well as in cosmetics and similar applications. Similarly, other polymeric porous complexes have also been used in fragrance delivery as a templating agent for aromatherapy textiles. Such polymeric materials offer an advantage in terms of development of new hybrid blends via homogenous mixing of two or more matrices. Such blends may possess different desirable physical properties as encapsulants. This review article is aimed at presenting an overview of polymers and their complexes as the main media of fragrance encapsulation. This study also discusses the expansion and future application of porous materials as host matrices for fragrances.

A three-phase copper MOF-graphene-polyaniline composite for effective sensing of ammonia

In this work, a three-phase composite material consisting of SiO2-coated Cu-MOF, single layer graphene, and aniline was synthesized. In the presence of ammonium persulfate as an oxidant, the aniline component of this mixture was polymerized to polyaniline to bridge Cu-MOF and graphene in the composite. Hence, a new sensory material with a highly porous nature (MOF) and superior conduction properties (graphene/polyaniline) was constructed. More specifically, the inclusion of Cu-MOF in the matrix facilitated the acquisition of an electrochemically active sensory material with a high surface area of about 756 m2/g. The potential application of this porous semiconducting material was demonstrated for sensitive detection of ammonia in a linear detection range over 1-100 ppm with a low limit of detection of 0.6 ppm.