Biohybrids for Environmental Remediation and Biosensing 271

engineered living bacteria was associated with hydrogel-elastomer hybrid matrix and support has

helped in growth of cells. A biohybrid comprising Silica-Sphingomonas sp. cells were immobilized

and used as a biosensor for detection of methyl parathion pesticide (Mishra et al. 2017). This

biosensor could detect methyl parathion in the linear range of 0.1 – 1 ppm concentration.

As reported, Rhodobacter sphaeroides reaction centre is a robust and tractable membrane

protein which has potential for technological applications and lead to develop biohybrid devices for

various applications like biosensing (Swainsbury et al. 2014). This study evaluated the viability of

using a tiny working electrode attached to a reaction centre to create a photocurrent as the basis for

a biosensor for classes of herbicides that are widely used to control weeds in important agricultural

crops. The triazides atrazine and terbutryn suppressed photocurrent production in a concentration-

dependent manner, but nitrile or phenylurea herbicides did not. The kinetics of charge recombination

in photo-oxidized reaction centres in solution were measured, and the results revealed the same

selectivity of response. The limits of detection were calculated to be about 8 nM and 50 nM,

respectively, as indicated in the Table 15.1. Titrations of the reaction centre photocurrents produced

half maximum inhibitory doses of 2.1 mM and 208 nM for atrazine and terbutryn, respectively.

Without the need for model-dependent kinetic analysis of the signal used for detection or the use

of unreasonably complex instrumentation, photocurrent attenuation provided a direct measure of

herbicide concentration. It also offered the possibility of using protein-engineering to increase the

selectivity and sensitivity of herbicide against the Rbasphaeroides reaction centre.

In the urban and rural regions of Campo Verde and Lucas do Rio Verde Cities, Mato Grosso

State, Brazil, Table 15.1 offers information on the prevalence of the pesticides atrazine, chlorpyrifos,

a-endosulfan, β-endosulfan, flutriafol, malathion and metolachlor in water bodies (Nogueira et al.

2012). In these significant grain-producing regions, samples of the surface, rain and groundwater

were taken throughout the wet and dry seasons of 2007 and 2008. The results showed that rainwater

had a greater variety of chemicals and a higher frequency of detection than surface and groundwater

samples. Some surface and groundwater samples contained concentrations of atrazine, endosulfan

and malathion that were higher than those prescribed by Brazilian regulations, and some samples

contained a higher amount of degraded product of deisopropylatrazine and endosulfansulfate

in comparison to their parent compounds. The results highlight the fragility of the local water

infrastructure and the danger of pesticide contamination in significant headwater streams.

15.7.2 Heavy Metal Monitoring and Remediation

The scarcity of drinking water due to increase of pollutants in water bodies is a matter of concern

(Mishra et al. 2021b, Mishra et al. 2022). Thus, remediation of pollutants from waste water is of

great significance for environment and human health. Among various techniques, bioremediation

and adsorption have wider applicability (Shukla et al. 2022). A large range of sorbents have been

applied for the removal of heavy metals. Among all nanosize silica have been widely applied for

sorption of radionuclide like uranium (Gabriel et al. 2001, Metilda et al. 2005). Nanoparticles have

many advantages however, their application as a sorbent has certain limitations such as harmful

impact on human health, the environmental fate of nanoparticles, and technical limitations like

difficulty in separation.

Several microbial systems have been used for bioremediation of heavy metals and radionuclide

like uranium (Sar et al. 2004, Kazy et al. 2009, Wang et al. 2010, Melo et al. 2020). However, poor

mechanical strength, a small size with low density and less rigidity of microorganism biomass are

the limiting factors (Wang et al. 2010). Association of biomass with a suitable support could be an

efficient way for improving its application for bioremediation. With this motive, microorganisms

and other biomolecules have been conjugated with suitable supports to develop biohybrids and used

as sorbents.

There has been a need for suitable methods for the preparation of biohybrids in large quantities.

Thus, the spray drying technique was applied to prepare a wide range of biohybrids using nanosilica