According to World Health Organization, 300 million people around the world are now suffering from depression and 10 million people are affected with Parkinson’s disease, which stems from the deficient release of dopamine in the human brain. However, precise quantification of dopamine secretion in the live human brain remains speculative because of the lack of a consistent technique to estimate dopamine neurotransmission. Therefore, precise quantification of dopamine neurotransmission in-vivo is the call of the time. In the present proposal, the experienced researcher (ER) would like to offer an opto-mechanical route to decipher the long-standing problem of dopamine detection by graphene oxide substrate sheets (GNGO’s). The present approach aims at taking advantage of the lattice defects present in graphene oxide (GO) sheets, where localized surface plasmons generate very intense electric fields, dramatically increasing the scattering signal coming from adsorbed and nearby molecules4. Such signals could be harnessed easily through surface-enhanced Raman spectroscopy (SERS). To incorporate this, the ER proposes to controllably bring GNDs close to the plasmonic pit holes on GO optomechanically using laser tweezers Raman spectroscopy (LTRS), creating a strong electromagnetic coupling that will boost the sensitivity towards dopamine. It has been anticipated that the effect will be sufficient to monitor the Raman shifts due to minute changes in dopamine concentration. In addition, we will explore how the local concentration of dopamine (or any other substance of interest) can be locally increased by inducing electro-thermo-plasmonic (ETP) flow taking advantage of the temperature gradient generated by the heat released at the hotspot. The project “SERS –tweezers enhanced by ElectroThermoplasmonic flow” (SERSET) promotes a simple, cost-effective, non-invasive and reproducible protocol to scale dopamine level. Available techniques for dopamine sensing largely rely on SERS, fluorometric, electrochemical and colourimetric principles. Through a vigorous survey of the literature, Scheme 1 represents the state-of-the-art in dopamine sensing, considering the five most efficient sensing protocols from all the aforementioned techniques, where the negative logarithm of limit of detection (LOD) is taken as the sensitivity parameter. Scheme 1 shows that sensors based on SERS are the most sensitive, and the proposed protocol aims to increase the sensitivity and reproducibility further with concerted electro-thermo-plasmonic (ETP) flow through LTRS. Therefore, the project SERSET aims to go beyond the current state-of-the-art methodology in terms of selectivity and consistency of SERS data, which has been a challenge for the past couple of decades. Table 1 elicits the gaps in state-of-the-art and innovative aspects of SERSET, which consists of the following staircase of objectives:
O1. The first objective is to synthesize GNGOs with DNA aptamer functionalized gold nanoparticles. Next, the optical signature of pristine GNGO through LTRS and emission spectroscopy will be studied as a function of the distance between gold monomers. Comparing the shift in SERS signal with the concentration of dopamine, a scale for the quantification of dopamine could be obtained, which has been depicted in work package 1 (WP 1). In the next work package (WP 2), ETP flow will be introduced to enhance the sensitivity of GNGO by employing a suitable AC electric field. The ER will acquire hands-on experience in state-of-the-art technology, increasing their core research skills.
O2. The next question naturally arises: what is the effect of GND distance on LTRS shift for a GNGO substrate? And, more significantly, what is the effect of carrier mobility towards the GNGO-dopamine interaction? To find these answers, the ER will study and model the system thoroughly through quantum and electromagnetic simulations in the secondment with Prof. Romain Quidant at ETH Zurich. This objective will lead to the design of a device prototype, which will be aimed at in the third work package (WP3), which will develop advanced research skills of ER.
O3. The final objective is to transfer the knowledge through diverse communication and dissemination activities.
