*Electrochemical Detection of Heavy Metals Based on Nanostructured, or Film-Modified Paper… DOI: http://dx.doi.org/10.5772/intechopen.109956*

measurements can be done at the same time. This way not only heavy metals, such as Cd (II), Pb (II), Zn (II), and Ni (II) can be determined, but also other metals, such as Fe (II) and Cu (II). The analysis of river samples was validated by comparison with results obtained by atomic absorption spectrometry. This method combined the flexibility of using paper platforms with their modification properties to detect multiple analytes by different principles. Miniaturization is also an important advantage, allowing to use lower volumes than the reference method.


### **Table 1.**

*Comparison of results of electrochemical analysis on paper-based platforms.*

Most of paper electrodes are made of carbon, but there are alternatives. C. Kokkinos et al. designed a microfluidic paper electrode with a working electrode composed of a sputtered film of tin (Sn) to determine Cd (II) and Zn (II) at trace levels with limits of detection of 0.9 and 1.1 μg/L, respectively [31]. The tin working electrode and the auxiliary and reference electrode were made by sputtering over the paper substrate. A microfluidic channel was printed on reverse paper. This helps to diffuse the samples, taking advantage of the capillarity. Volumes as low as 10 μL could be used.

All mentioned reports show a variety of options for designing paper electrochemical cells for heavy metal determination. **Table 1** resumes all the results previously commented. All of them contribute to the goal of low-cost, sustainable, easy-to-use, and green analytical platforms. This is especially attractive for use in underdevelopment countries or in places in which portability and rapidity are the main requirements.
