Periodic Reporting for period 1 - SERSET (SERS –tweezers enhanced by electro-thermo-plasmonic flow)
Reporting period: 2023-02-01 to 2025-05-31
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.
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.
The overall project is divided into several work packages, which have been perceived sequentially
WP1. Synthesis & optical signature of pristine GNGO: For the initial development, we have synthesized Gold nanoparticles (GNP) and a Graphene oxide-PVDF composite in the wet chemical method, which has been used as the 2D substrate. The gold nanoparticles has beeen trapped with the NIR laser beam and carefully brought into the LSPR pit of GO surface. The Raman signals are recorded for the primary interaction. This experimental protocol will constitute an original approach towards state-of-the-art analytical techniques. This cross-disciplinary protocol where the optical forces will be exploited to synthesize GNGO and set up the baseline of AuNP-GO interaction measuring LTRS and emission, has been depicted as the first work package (WP1). According to the proposed protocol, we have synthesized different sets of nanospheres and gold nanorods with different aspect ratios. It was found that, with the label-free condition, we can also sense dopamine using the same principle. We have trapped successfully the gold nanoparticles to bring them close to the graphene oxide surface to generate a strong gap electromagnetic interaction, which can give rise to strong SERS.
WP2. LTRS and emission spectroscopy of dopamine-GNGO interaction: In the next step, we have scaled the effect of dopamine concentration through LTRS and trapped emission characteristics. Also, from LTRS spectroscopy, the shift in the Raman signal shows the bonding characteristics of dopamine with GNGO, with and without the formation of the bubble inside the cell. Through this multidisciplinary interdigitation process, we have documented the chemical interaction between dopamine and GNGO through the Raman shift observed on a very small timescale. The response of such light-matter interaction has been modelled to generate a digital response of SERS as a function of dopamine concentration, which forms the basis of the second work package (WP2). This cross-disciplinary interdigitation process renders the optical conductivity of GNGO as a function of the Raman and emission wavelength shift with the concentration of dopamine.
WP3. Simulations and modelling: We have theoretically analyzed the effects of dopamine concentration on LTRS. It has been recently demonstrated that these changes are translated into measurable variations of the force that the optical tweezers can exert on the particle. From LTRS data of pristine GNGO, the shift in the vibrational level of pristine graphene oxide and their emission intensity can be deduced as a function of the distance between neighbouring trapped GND and GO surface, as proclaimed in O1. SERS enhancement factor (EF) is strongly dependent on the localized field, and we can modulate the distance between trapped GNP s and the
For a range of dopamine concentrations, the change in dipole (Δµ) and shift in polarizability (α) can be calculated through experiment and density functional theory. The theoretical evaluation of polarizability, will allow for the comparison of the simulations with the experiments on trapping efficiency under different conditions. This model would form the equation to interconnect chemical bonding and the force exerted by the optical tweezers on the trapped GND. Converging the experiments with theory, the study signifies an interdisciplinary approach to interconnect LTRS and emission during GNGO-dopamine interaction and develop a response function which will be used as a scale for LTRS-mediated sensing of dopamine as per objective O2. The theoretical work will be done through the planned secondment with Prof. Romain Quidant at ETH Zurich, who is a world leader in plasmonic sensing. In this interdisciplinary scaling protocol, the ER would decipher the effect of dopamine concentration on LTRS as a function of trapping position, and monomer distance and combine optical trapping parameters with emission intensity through individual scaling.
WP1. Synthesis & optical signature of pristine GNGO: For the initial development, we have synthesized Gold nanoparticles (GNP) and a Graphene oxide-PVDF composite in the wet chemical method, which has been used as the 2D substrate. The gold nanoparticles has beeen trapped with the NIR laser beam and carefully brought into the LSPR pit of GO surface. The Raman signals are recorded for the primary interaction. This experimental protocol will constitute an original approach towards state-of-the-art analytical techniques. This cross-disciplinary protocol where the optical forces will be exploited to synthesize GNGO and set up the baseline of AuNP-GO interaction measuring LTRS and emission, has been depicted as the first work package (WP1). According to the proposed protocol, we have synthesized different sets of nanospheres and gold nanorods with different aspect ratios. It was found that, with the label-free condition, we can also sense dopamine using the same principle. We have trapped successfully the gold nanoparticles to bring them close to the graphene oxide surface to generate a strong gap electromagnetic interaction, which can give rise to strong SERS.
WP2. LTRS and emission spectroscopy of dopamine-GNGO interaction: In the next step, we have scaled the effect of dopamine concentration through LTRS and trapped emission characteristics. Also, from LTRS spectroscopy, the shift in the Raman signal shows the bonding characteristics of dopamine with GNGO, with and without the formation of the bubble inside the cell. Through this multidisciplinary interdigitation process, we have documented the chemical interaction between dopamine and GNGO through the Raman shift observed on a very small timescale. The response of such light-matter interaction has been modelled to generate a digital response of SERS as a function of dopamine concentration, which forms the basis of the second work package (WP2). This cross-disciplinary interdigitation process renders the optical conductivity of GNGO as a function of the Raman and emission wavelength shift with the concentration of dopamine.
WP3. Simulations and modelling: We have theoretically analyzed the effects of dopamine concentration on LTRS. It has been recently demonstrated that these changes are translated into measurable variations of the force that the optical tweezers can exert on the particle. From LTRS data of pristine GNGO, the shift in the vibrational level of pristine graphene oxide and their emission intensity can be deduced as a function of the distance between neighbouring trapped GND and GO surface, as proclaimed in O1. SERS enhancement factor (EF) is strongly dependent on the localized field, and we can modulate the distance between trapped GNP s and the
For a range of dopamine concentrations, the change in dipole (Δµ) and shift in polarizability (α) can be calculated through experiment and density functional theory. The theoretical evaluation of polarizability, will allow for the comparison of the simulations with the experiments on trapping efficiency under different conditions. This model would form the equation to interconnect chemical bonding and the force exerted by the optical tweezers on the trapped GND. Converging the experiments with theory, the study signifies an interdisciplinary approach to interconnect LTRS and emission during GNGO-dopamine interaction and develop a response function which will be used as a scale for LTRS-mediated sensing of dopamine as per objective O2. The theoretical work will be done through the planned secondment with Prof. Romain Quidant at ETH Zurich, who is a world leader in plasmonic sensing. In this interdisciplinary scaling protocol, the ER would decipher the effect of dopamine concentration on LTRS as a function of trapping position, and monomer distance and combine optical trapping parameters with emission intensity through individual scaling.
The project has opened some new pathways in the sensing of dopamine in several ways:
1. We have successfully defined the interaction between gold nanoparticles and dopamine within the framework of Laser Tweezers Raman Spectroscopy, which constitutes a NEW METHODOLOGY using the plasmonic interaction between graphene oxide and gold nanoparticles.
2. We have developed a sensor which can sense dopamine at a single molecular limit with a very small sample volume of below 10 microliters.
3. We have also investigated the mechanism of the growth of nanorods in a wide range of systematic studies. We found a new relationship between the pH of the medium and the aspect ratio of the nanorods formed during a long set of data pertaining to the experiments performed.
1. We have successfully defined the interaction between gold nanoparticles and dopamine within the framework of Laser Tweezers Raman Spectroscopy, which constitutes a NEW METHODOLOGY using the plasmonic interaction between graphene oxide and gold nanoparticles.
2. We have developed a sensor which can sense dopamine at a single molecular limit with a very small sample volume of below 10 microliters.
3. We have also investigated the mechanism of the growth of nanorods in a wide range of systematic studies. We found a new relationship between the pH of the medium and the aspect ratio of the nanorods formed during a long set of data pertaining to the experiments performed.