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Due to the versatile usage and applications of chromium compounds in the industry worldwide, the chromium ions are present in the major effluents from a broad range of industries. Cr(VI) which is highly hazardous and carcinogenic poses a serious threat to the our ecosystem and human health even at very low concentration limits. Cr(III) ions are also toxic to aquatic life, but they are less harmful than Cr(VI) ions. Therefore, detection and analysis of the toxic Cr(VI) and Cr(III) ionic species in waste water are an utmost important area of research. Various chemical reagents and the different methods which require expensive instrumentation used in the past for detection and determination of the non-biodegradable Cr(VI) ions suffer from serious limitations. The present review summarises the use of spectrophotometric methods of determination of Cr(VI) and Cr(III) ions from aqueous solutions with high sensitivity, selectivity, accuracy and at lesser costs. The use of chemical reagents such as diphenylcarbazide (DPC) and several other dye-based reagents for spectrophotometric determination of hazardous Cr ions in water samples is discussed. Additionally, the use of DPC reagent in developing advanced technologies such as microfluidic detection system, microfluidic paper-based analytical devices (µPADs) and 3D printed device with online spectrophotometric detection system for onsite monitoring of water samples is elucidated. Different methods for selective speciation and preconcentration of Cr(VI) ions prior to spectrophotometric determination in water samples with very low concentrations (as low as ppb) of Cr ions are also described. The emerging trends in detection and determination of carcinogenic Cr(VI) ions involving the use of novel and innovative technologies and different categories of nanomaterials are also elucidated in the present review. [ABSTRACT FROM AUTHOR]

• Graphene oxide (GO) has potential applications in biomedical fields. • The functionalization of graphene include two general routes i.e. covalent and non-covalent functionalization. • GO with different surface functionalization has been used as nano- carriers for loading of chemotherapy drugs. • GO-based smart drug delivery systems responsive to environmental stimulations have also been studied. The field of nanoscience has blossomed over the last two decades and the importance of nanotechnology has increased in areas such as computing, sensors, biomedicine, and many other applications. In the present study, recent important advances in the functionalization of graphene with an emphasis on the physical properties upon tailored modification have been reviewed. It has been observed that functionalization cannot only stabilize graphene's unique properties but also introduce some new properties. The functionalization of graphene can be done with different methods like covalent functionalization, non-covalent functionalization, and with the decoration of nanoparticles. In this study, we put forward functionalization of graphene by polymers with different methods such as by direct linking of polymeric chains to the graphene surface or by the controlled growth of the polymeric chains at graphene surface or by decorating with polymers. The exceptional in-plane properties of graphene that are more complete exfoliation of graphite towards single graphene sheets with excellent mechanical, thermal, electrical, and barrier properties. The biological applications for the treatment of deadly diseases like cancer by functionalized nano-graphene oxide (NGO) have reviewed in depth. The application of NGO for drug delivery for gene therapy treatment has also been discussed in this review. [ABSTRACT FROM AUTHOR]