This review tries to summarize the purpose of steadily developing surface-functionalized nanoparticles for various bio-applications and represents a fascinating and rapidly growing field of research. Due to their unique properties—such as novel optical, biodegradable, low-toxicity, biocompatibility, size, and highly catalytic features—these materials are considered superior, and it is thus vital to study these systems in a realistic and meaningful way. However, rapid aggregation, oxidation, and other problems are encountered with functionalized nanoparticles, inhibiting their subsequent utilization. Adequate surface modification of nanoparticles with organic and inorganic compounds results in improved physicochemical properties which can overcome these barriers. This review investigates and discusses the iron oxide nanoparticles, gold nanoparticles, platinum nanoparticles, silver nanoparticles, and silica-coated nanoparticles and how their unique properties after fabrication allow for their potential use in a wide range of bio-applications such as nano-based imaging, gene delivery, drug loading, and immunoassays. The different groups of nanoparticles and the advantages of surface functionalization and their applications are highlighted here. In recent years, surface-functionalized nanoparticles have become important materials for a broad range of bio-applications.

The key pathways for synthesizing nanoparticles are physical and chemical, usually expensive and possibly hazardous to the environment. In the recent past, the evaluation of green chemistry or biological techniques for synthesizing metal nanoparticles from plant extracts has drawn the attention of many researchers. The literature on the green production of nanoparticles using various metals (i.e., gold, silver, zinc, titanium and palladium) and plant extracts is discussed in this study. The generalized mechanism of nanoparticle synthesis involves reduction, stabilization, nucleation, aggregation and capping, followed by characterization. During biosynthesis, major difficulties often faced in maintaining the structure, size and yield of particles can be solved by monitoring the development parameters such as temperature, pH and reaction period. To establish a widely accepted approach, researchers must first explore the actual process underlying the plant-assisted synthesis of a metal nanoparticle and its action on others. The green synthesis of NPs is gaining attention owing to its facilitation of the development of alternative, sustainable, safer, less toxic and environment-friendly approaches. Thus, green nanotechnology using plant extract opens up new possibilities for the synthesis of novel nanoparticles with the desirable characteristics required for developing biosensors, biomedicine, cosmetics and nano-biotechnology, and in electrochemical, catalytic, antibacterial, electronics, sensing and other applications.

This review deals with the mechanism of antagonistic action of bacterial and fungal biocontrol agents such as the production of antibiotics, siderophores, enzyme secretion, competition for nutrition, plant growth promotion by rhizosphere microorganism. The utilisation of synthetic pesticides has been the predominant control processor for diseases brought about by phytopathogenic microorganisms. Notwithstanding, their open and improper application in intensive agriculture has realised issues that have prompted ecological contamination, considerable residues in agricultural products and phytopathogen resistance. They are likewise disrupting the quantity of beneficial microorganism which is available in the soil and capable of expanding soil fertility. Along these lines, there is a need to look through the option of synthetic pesticides that are safe, environmental and monetarily feasible to confront this problem. Biocontrol agent’s utilisation is the best alternative method to control the different kinds of diseases, such as nematode infestation, fungal pathogen and bacterial pathogen. Nowadays, biocontrol agents assume a significant role in the field of agriculture. It is a financially savvy, environment-friendly and inhibits the advancement of pathogenic microorganism sustainably. This review emphasises the role of biocontrol agents against different pathogenic microorganisms and their significance potentiality to improve plant growth and enhance defence system of plants.

In this study effort was made to manage the root-knot nematode, Meloidogyne incognita by the utilization of selected plants such as Coccinia grandis, Commelina benghalensis, Leucas cephalotes, Phyllanthus amarus and Trianthema portulacastrum. During the in vitro experiment, the second juveniles (J2s) of M. incognita directly treated with aqueous extracts of the plant leaves at 1000, 2000, 3000, 4000 and 5000 ppm concentrations. As a result, the 5000 ppm concentration was found most toxic against the survival of second stage juveniles of M. incognita compared to other concentrations. Maximum mortality of 91% was observed in 5000 ppm extract of P. amarus after 72 h of exposure with LC50 value 2084.49 ppm while minimum mortality of 6.2% was found in 1000 ppm extract of T. portulacastrum after 24 h with LC50 value 9484.18 ppm. The percent mortality of juveniles calculated the LC50 values of all the treatments after 24, 48 and 72 h. Similarly, the in vitro tests showed a gradual decrease in the rate of egg hatching of M. incognita with the increasing concentrations of aqueous leaves extracts of plants, i.e., 1000 ppm to 5000 ppm and exposure period. Maximum inhibition in egg hatching was found at 5000 ppm (86.5%) after seven days in the extract of P. amarus while least was observed in T. portulacastrum at 1000 ppm (10.6%). The findings indicate that the plant extracts were found lethal to J2s and also inhibit egg hatching. In pots under greenhouse conditions, the plants treated with both the doses (50 and 100 g/pot) of fresh chopped leaves of the selected botanicals significantly experienced the reduced infestations in relation to root gall index, egg masses/root system and nematode population/250 g soil. The P. amarus treated at 100 gm / pot showed highest nematicidal efficacy with the maximum reductions in all the pathological parameters as compared to the untreated uninoculated control simultaneously resulted in maximum increase of growth and physiological parameters of carrot such as shoot and root lengths, shoot and root fresh weights, shoot and root dry weights, chlorophyll and carotenoid contents and nitrate reductase activity (NRA). The information derived from this study suggests that the leaves of P. amarus plant can be used for the management of M. incognita and could be a possible replacement for synthetic nematicides.

The present investigation was carried out to evaluate the potential of chitosan alone and in combination with various agricultural wastes for the management of rootknot nematode, Meloidogyne incognita on eggplant cv. ‘BR-112’ under greenhouse conditions. The results showed that chitosan as a single or joint treatment with agricultural wastes significantly (p ≤ 0.05) reduced root-knot indices, and the nematode population in soil. As a result, of this, the growth and growth yielding attributes of eggplant were remarkably augmented. Chitosan as an elicitor induced plant mediated systemic resistance against M. incognita in eggplant. The results of the study demonstrated that maximum reduction in eggmass/root, eggs/eggmasses, nematode population and root-knot indices, was acquired by the treatments: chitosan + onion and chitosan + mentha. It was followed by chitosan + Brassica, chitosan + urad and chitosan + coconut whereas, chitosan combined with corn cob waste was found to be the least effective when compared to the control. The application of chitosan alone was effective but not very satisfactory. Compared to the control applications of all the treatments significantly increased plant growth in terms of length, fresh and dry weights, pollen fertility, yield and biochemical parameters such as chlorophyll, carotenoid content and antioxidant enzymes. This may have been due to the eliciting activity of chitosan, causing systemic resistance in the plant and the release of various toxic chemical compounds during decomposition which have lethal effects against the second stage juveniles of M. incognita and nematode multiplication.