**4. Applications**

*Biosensors for Environmental Monitoring*

for the antibody 12F6-AuNP conjugate, as the antibody 12F6 has an increased affin-

Biomolecules aiming the detection of toxic metals can also be referred. A complex comprising magnetic beads, gold nanoparticles (AuNPs), and the functional nucleotide GR5-DNAzyme was applied as a biorecognition element of lead ion [20]. In another work, the recombinant human metallothionein 1a, a metal-binding protein [18], was used for the recognition of As3+ and Hg2+ in water. The tetrameric protein lectin concanavalin A (obtained from *Canavalia ensiformis*), selective to carbohydrates on bacterial cells, was selected as a biorecognition element of bacterial

Finally, whole-cell living bacterial biosensors for arsenite detection were based on genetically engineered *E. coli*, where the *ars* operon (set of structural and regulatory genes whose expression is controlled through arsenite binding) was modified with a sequence for expression of β-galactosidase as a reporter protein in the presence of the target analyte [30]. Whole cells (biofilm formed from anaerobic sludge) were also employed in the biosensor proposed by Chouler et al. [25] for the assessment

ity to U(VI)-2,9-dicarboxyl-1,10-phenanthroline complex [24].

*Examples of biorecognition elements found in paper-based biosensors.*

cultures from sewage sludge [27].

**86**

**Figure 2.**

In this section, the application of paper-based biosensors for the detection of different types of target analytes in water samples is discussed. In **Table 2**, the main features of the target analyte, the sample type, the paper substrate, and the fabrication method of the paper-based device, the method of detection, and the biorecognition element are summarized.

Pharmaceuticals are among the targets. Indeed, they are considered emerging environmental contaminants, as they can be harmful to human health and to aquatic life. In this context, the synthetic hormone—ethinylestradiol, one of the main compounds of oral contraceptives, is considered an emerging pollutant due to its potential high estrogenic effect on the biota. Scala-Benuzzi et al. developed two different methods for the detection of ethinylestradiol in river water samples using an antiethinylestradiol specific antibody [16, 17]. In both approaches, the water samples were filtered, and pH was adjusted to 7.0 with phosphate buffer before the analysis. In one work, a fluorescent paper-based biosensor was implemented [16]. This methodology presented a limit of detection (LOD) of 0.05 ng L<sup>−</sup><sup>1</sup> , which is mainly related to the high sensitivity of fluorescence methods. In another work, ethinylestradiol was detected in river water with a paper-based immunosensor based on electrochemical analysis [17], which also reached a low LOD value of 0.1 ng L<sup>−</sup><sup>1</sup> , suitable for environmental analysis.

Antibiotics are another group of pollutants of great concern due to the global threat of antimicrobial resistance and the excessive, and sometimes abusive, use of these compounds. A colorimetric biosensor for screening of several antibiotics (paromomycin, tetracycline, chloramphenicol, and erythromycin) inhibiting bacterial protein synthesis was applied for the detection of antibiotics in surface water [19]. The method was based on the ability of these antimicrobials to inhibit β-galactosidase synthesis. When a water sample without the target antibiotics was placed in the paper-based device, the enzyme β-galactosidase was synthetized and its activity induced a color change on the paper disc surface. However, when antibiotics were present, the inhibition of β-galactosidase synthesis prevented the change of color. Despite the limit of detection was on the microgram per milliliter level (0.5, 2.1, 0.8, and 6.1 μg mL<sup>−</sup><sup>1</sup> for paromomycin, tetracycline, chloramphenicol, and erythromycin, respectively), this biosensor can be applied as a simple and portable screening methodology.

Heavy metals are naturally present in the environment. However, these elements can be toxic to human and aquatic organisms even at low concentrations. Moreover, their presence can be increased by industrial and agriculture activities. Vijitvarasan et al. implemented a paper-based scanometric biosensor for the detection of lead in water [20]. The biosensor was applied to river water samples. These samples were filtered, diluted 10 times with 10 mM tris-acetate buffer and spiked with different Pb2+ concentrations before analysis. An LOD value of 0.9 nM was determined. Furthermore, a method using a sensitive gold nanoparticle-based lateral flow immunodevice [23] was applied for the quantification of cadmium. Drinking water


**89**

**Target** E. coli, *Enterococcus* spp.

Others Water toxicity

Lagoon water, alfalfa sprout

Artificial wastewater

Shock pollution

*aParomomycin, tetracycline, chloramphenicol, and erythromycin.*

*bLOD value for E. coli.*

*cLOD value for Zika virus.*

*dLOD value for Zika virus expressed as transcription copies mL−1*

*eFormaldehyde concentration monitored (% v/v).*

*fPower output slope for Cr (VI).*

**Table 2.**

*Paper-based biosensors for analysis of pharmaceuticals, heavy metals, and waterborne pathogens in water.*

*.*

Wastewater

Filter paper; ink coating

*F, fluorescence; E, electrochemical; C, colorimetric; P, photometric; R, rheology-based measurement. PNP: p-nitrophenol; ONP: o-nitrophenol.*

E

Bacteria consortium

0.022f

[26]

Cotton-based paper; screen printing

E

Biofilm formed from anaerobic sludge

0.1e

[25]

**Sample type**

**Paper substrate; fabrication method**

Multiuse recycled copy paper; wax printing

C

Substrates ONP and PNP

81 μM (ONP), 119 μM (PNP)

[28]

**Detection method**

**Biorecognition element**

**LOD**

**Reference**

*Paper-Based Biosensors for Analysis of Water DOI: http://dx.doi.org/10.5772/intechopen.84131*

*Biosensors for Environmental Monitoring*

