Adjusting Paper Device Properties for Bioelectrochemical Analysis and 3D Cell Culture
Authors: Pelletier Juliette , Trouillon Raphaël 
Published: August 2024

Context- Paper is an innovative material for cell culture due to its biocompatibility, its inert chemical properties and its low-cost. Paper is already used in many biomedical applications such as immunoassays and, more recently, as affordable electrochemical sensors. In this context, tuning the properties of paper devices can achieve better, more efficient and user-friendly assays for biomedical applications. Here, and by modifying the electrochemical properties of paper electrochemical devices, it is possible to create electrodes that can detect neurotransmitters, a critical type of biomolecules involved in neuronal communication. Dopamine is a neurotransmitter involved in reward and addiction and a molecule of considerable scientific interest. Dopamine is secreted in the brain by dopaminergic neurons. However, the fine chemical mechanisms of neuron networks are still obscure. Being able to spatially measure dopamine secretion, in response to activation of precise neuronal regions in a unique system, can lead to a better understanding of neuronal dynamics, as well as their response to drug alterations. Proposing a research model describing neuronal chemical function in a network will therefore help shining light on their mechanisms and testing new neuropharmacological solutions. Developing new tools for the analytical electrochemistry of the brain will make quantitative neuro-analysis more accessible, thus paving the way for a better understanding of the chemical mechanisms of the brain.

Tuning paper electrode for neurochemical analysis- Conductive inks, i.e. conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) and carbon nanotubes (CNT) suspensions, were used to improve the detection of dopamine at paper-based electrodes. The physical and chemical properties of different preparations and mixtures of inks were considered. Solvent secondary doping, a common technique for PEDOT-PSS based electrode, was used to improve the electrical properties of the electrodes. Ferrocyanide electroanalysis was used to benchmark 10 different electrode preparations, revealing that combining CNT and PEDOT-PSS improves the electroactivity of the surface of the sensor. Interestingly, it was found that CNT has a doping effect on PEDOT-PSS, leading to improved electrochemical properties. Finally, these electrodes were tested for dopamine detection. It was found that combining PEDOT-PSS and CNT in the surface layer of ink deposited on the paper electrode allows for lower capacitance, higher anodic current as well as better fouling resistance. Figure 1 presents a CV voltammogram for Dopamine obtained with a paper electrode. Overall, this strategy improves the sensitivity of the assay.

Growing neurons on paper- Paper-based devices can also be used for cell culture. Cell on paper constructs are 3D cell culture models that are more suitable to study cell in a biomimetic 3D environment, thus better recapitulating their functions and biology. By carefully modifying the surface of the paper devices, it is possible to adjust their biocompatible properties to ameliorate the survival rate of cell culture on paper. This opens the possibility to achieve neuronal cell culture on paper. We will present different paper preparations compatible with murine dopaminergic maintenance. The neurons were maintained alive for several days of culture. We were able to effectively observe and study neurons in a 3D paper environment and quantify the growth of their processes.

Figure 1 : Electrochemical detection of Dopamine for 20 cycles. Working electrode is a paper electrode with PEDOT:PSS and CNT conductive inks, shown on the right, scale is 1 cm. The reference electrode is an Ag/AgCl electrode, and the counter electrode is a platinum electrode. Scan rate is 0.02 Vs-1.

Figure 1