# Inkjet-Printed and Paper-Based Electrochemical Sensors
## 5 Conclusions  
Ordinarily, innovation implies production of new materials, creation of new methods, and establishment of new procedures. This is certainly evident with many technological advancements, but it does not truly encompass the meaning of innovation. Innovation requires novelty, of course, \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Electrode** & **Microfluidic Fabrication** & **Ink** & **Electrode Modification** & **Target Analyte** & **LOD 1** & **Ref.** \\ \hline \multirow{6}{*}{**Inkjet printing**} & PDMS 1 casting & Gold & Glucose oxidase & Glucose & 0.1 mM & [14] \\ \cline{2-7}  & Inkjet-printed & Carbon & & & & \\ mineral oil & nanotubes & & & & & \\ \cline{2-7}  & Mineral oil casting & Carbon & & & & \\  & & nanotubes & & & & \\ \cline{2-7}  & - & Gold NPs 1 & - & Oxygen & 0.0075\% & [42] \\ \hline \multirow{6}{*}{**Screen Printing**} & Photolithography & Carbon & \begin{tabular}{c} Sodium dodecyl \\ sulfate \\ \end{tabular} & Dopamine & 0.37 mM & [21] \\ \cline{2-7}  & \multirow{2}{*}{Wax printing} & Carbon & \
\begin{tabular}{c} Graphene, \\ Polyvinylidene, \\ Polyaniline, \\ Cholesterol oxidase \\ \end{tabular} & Cholesterol & 1 uM & [22] \\ \cline{2-7}  & \multirow{2}{*}{Wax printing} & \multirow{2}{*}{Carbon} & 3-HBDH, NAD+ 1 & Beta-hydroxybutyrat0.3 mM & [23] \\ \cline{2-7}  & \multirow{2}{*}{Wax printing} & Carbon & - & Lead, Cadmium & 1 ug/L & [11] \\ \cline{2-7}  & Photolithography & Carbon & & Gold & 5.07 mM & [24] \\ \cline{2-7}  & \multirow{2}{*}{Wax printing} & \multirow{2}{*}{Carbon} & Glucose oxidase, & \multirow{2}{*}{Glucose} & \multirow{2}{*}{9.3 uM} & [25] \\ \cline{2-7}  & Multilayer paper & & Platinum NPs & & & \\ \cline{2-7}  & \multirow{2}{*}{-} & \multirow{2}{*}{Carbon} &
\begin{tabular}{c} Cobalt(II) \\ phthalocyanine \\ \end{tabular} & \multirow{2}{*}{1-butanethiol} & \multirow{2}{*}{0.5 uM} & [12] \\ \hline
**Screen and** \\
**inkjet printing** & Wax casting &
\begin{tabular}{c} Carbon, \\ polyaniline \\ \end{tabular} & - & Ascorbic acid & 30 uM & [43] \\ \hline \end{tabular}  
* 1 LOD: Limit of Detection; PDMS: Polydimethylsiloxane; NPs: Nanoparticles; NAD+: Oxidized Nicotinamide Adenine Dinucleotide.  
\end{table} 
Table 1: Summary of previous works on paper-based electrochemical sensors. but it would be better to describe innovation in a more general way. In fact, innovation could be simply described as the ability to perform a given task in a new way. Thus, it is not necessarily limited to the use of new materials or new methods. As discussed throughout this review article, the majority of materials, methods, and procedures are not particularly new or novel. Rather, it is the application of these materials and technologies that suggests innovation. The application and need discussed here is that of low cost point-of-care devices for biological and chemical sensing. By focusing on established materials and fabrication techniques, inkjet-printed paper-based electrochemical sensors can be produced with minimal cost allowing for devices that truly meet the needs of patients and the medical community. It is also very likely that these devices will be considered disposable if the cost is low enough. Throughout this review article, alternatives are discussed--sometimes at length--in order to provide a valid comparison between each of the presented materials and methods. With respect to fabrication methods, inkjet printing and screen printing are indeed the most common methods used today. Each of these methods have been used to fabricate impressive electrochemical devices, but inkjet printing does have a few noteworthy advantages when compared to screen printing. Inkjet printing obviously does not require templates, which saves time and production cost. Additionally, material thickness can be controlled very easily and multiple materials can be deposited simultaneously with inkjet printing. In terms of materials, conductive nanomaterials were primarily used regardless of fabrication method.