**4. Paper based optical and electrochemical sensing of HMIs**

It is striking from the above discussions that both electrochemical and optical methods are good enough to quantify HMIs from various sample matrices. Selectivity, sensitivity and reproducibility of the most of the methods are sufficient enough i.e. can be used to quantify the HMIs within the permissible limits fixed by the world health organization. Apart from this there are some shortcomings for both the methodologies. It must be noted that both the instruments i.e. classical potentiostat and spectrophotometer cannot be carried away to the place at which the samples have to be analyzed. Hence, spot analysis of the HMIs is quite not possible using these methods. Also, both the instruments are expensive. Keeping these shortcomings in mind researchers are working out nonconventional methods. As it is already mentioned in **Table 1** miniaturized potentiostat and spectrophotometers are developed for spot analysis. Affordable and mobile phone installable softwares are developed to readout the color intensity on the spot [82]. On the other hand, sample holders i.e. electrochemical cells and cuvettes are replaced by paper strips. Below is the glimpse of such non-trivial methods.

*Electrochemical and Optical Methods for the Quantification of Lead and Other Heavy Metal… DOI: http://dx.doi.org/10.5772/intechopen.95085*
