Quantifying Surface Temperature of Thermoplasmonic Nanostructures

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Quantifying Surface Temperature of Thermoplasmonic Nanostructures Shu Hu, Bi-Ju Liu, Jia-Min Feng, Cheng Zong, Kai-Qiang Lin, Xiang Wang, De-Yin Wu, and Bin Ren J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b06083 • Publication Date (Web): 03 Oct 2018 Downloaded from http://pubs.acs.org on October 3, 2018

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Journal of the American Chemical Society

Quantifying Surface Temperature of Thermoplasmonic Nanostructures Shu Hu,† Bi-Ju Liu,† Jia-Min Feng,† Cheng Zong, Kai-Qiang Lin, Xiang Wang, De-Yin Wu, Bin Ren* State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (i-ChEM), The MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China. ABSTRACT: Precise measurement of the temperature right at the surface of thermoplasmonic nanoparticles is a grand challenge but extremely important for the photochemical reaction and photothermal therapy. We present here a method capable of measuring the surface temperature of plasmonic nanostructures with surface-enhanced Raman spectroscopy (SERS), which is not achievable by existing methods. We observe a sensitive shift of stretching vibration of phenyl isocyanide (PIC) molecule with temperature (0.232 cm-1/ºC) as a result of the temperature-dependent molecular orientation change. We develop this phenomenon into a method capable of measuring the surface temperature of Au nanoparticles (NPs) during the plasmonic excitation, which is validated by monitoring the laser-induced desorption process of the adsorbed CO on Au NPs surfaces. We further extend the method into a more demanding single living cell thermometry that requires a high spatial resolution, which allows us to successfully monitor the extracellular temperature distribution of single living cell experiencing cold resistance and the intracellular temperature change during the calcium ion transport process.

INTRODUCTION The excitation of the surface plasmon resonance of Au, Ag and Cu NPs will lead to an enhanced absorption of the visible light and increased yield of “hot” electrons.1-9 The produced hot electron and the significant thermal effect during the dephasing process of excited electron may trigger or accelerate some chemical reactions at the plasmonic NP surface, which is important to plasmon-enhanced chemical reaction and photothermal therapy.10 Impressively, a new field called thermoplasmonics comes to form.11-13 The interaction between the “hot” electron and the phonon of NPs increases the lattice temperature, and the lattice vibration of the NPs decays by transferring energy to the environment to increase the temperature of the environment usually within the time scale of nanosecond.14,15 With this understanding, it is not surprising that the local temperature on the NP surface will be much higher than that in the bulk solution. As the heterogeneous chemical reaction usually occurs on the NP surface and the living cells are in contact with the NP surface, we would expect the real plasmon-induced photothermal effect on the NP surface will be greater than that of the bulk temperature measured with thermometer after the illumination of light. For example, the solar illumination of Au NPs led to the generation of steam while the solution was still cold.16 It was also found that although Au NPs did not produce perceptible temperature rise in the cells, the heating effect close to the surface was still able to kill the cell.17 Therefore, it is vitally important to measure the surface temperature of NPs to adequately evaluate the role of photothermal effect in photothermal therapy,17,18 photovoltaics,19,20 photocatalysis,21,22 and intracellular cell biological processes.23,24 Various optical methods, including infrared spectroscopy, interferometry, fluorescence microscopy, and luminescent of nanoparticles, have been successfully developed to probe the local temperature.25,26 Nanostructures (such as lanthanide iondoped NPs,27 plasmonic nanostructures28 and nanodiamonds29)

used for determining the temperature were called nanothermometers. Different from the name, the nanothermometers are still not able to achieve spatial resolution better than the diffraction limit and the measured temperature is rather the average effect of nanostructures with its adjacent surrounding environment than that right at the surface of nanostructures. Although scanning thermal microscopy can be used for surface temperature measurement,30 many parameters, including surface features and complicate heat transfer between the tip and substrate, may affect the accuracy of such a measurement. Therefore, development of a simple, non-contact, and reliable thermometry for measuring the temperature right at the surface of thermoplasmonic nanostructure is still strongly required. Raman microscopy has also been used to measure the temperature, by using the intensity ratio change of the Stokes and anti-Stokes Raman peaks with temperature or the frequency change of some materials like silicon, gallium nitride, carbon nanotube, and graphene as a result of the lattice expansion and compression.31-34 Due to the weak Raman signal of molecular species and a small frequency shift of bulk materials (0.02 cm1 /ºC), it is still very challenging to use Raman microscopy for surface or microscale temperature sensing.31,34 Surface- or tipenhanced Raman spectroscopy (SERS or TERS) has also been used to measure the surface temperature, which all relied either on the absolute intensity or the intensity ratio of two Raman peaks (including the use of Stokes and anti-Stokes Raman peaks).35-38 However, the two-fold enhancement mechanism of SERS (excitation and emission enhancements) determines that the SERS relatively intensity will be modified by the plasmonic spectral shaping effect (PSSE) (see our previous work).39 Such an effect will vary with temperature (will lead to the interparticle distance change) and coupling state of nanoparticles (will be affected by the temperature and vary from spot to spot on the SERS substrate). As a result, it was commonly found that different regions of a substrate at a same temperature gave SERS spectra with largely different relative

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Figure 1. Temperature sensing using PIC molecules adsorbed on Au NPs surface. (A) Schematic of temperature-dependent SERS measurement and temperature induced orientation change of PIC molecules. (B) Temperature and (C) laser power dependent SERS spectra of PIC in the spectral range of the N≡C stretching vibration; (D) Raman shift and FWHM of the N≡C peak as a function of temperature. (E) Raman shift of the N≡C peak as a function of laser power. The laser power used in (B) was 2.67 µW.

peak intensity. If no PSSE is properly corrected, the use of SERS intensity to measure the temperature may lead to a significant error on the determined temperature.40 Therefore, it is important to find an alternative method that can monitor the temperature right at the surface of NPs for practical applications. In this work, we develop a novel method to measure the temperature right at the surface of NPs by using the frequency shift of N≡C stretching vibration of phenyl isocyanide (PIC) adsorbed on Au NPs surface. This peak frequency shows strongly dependence on temperature, which has never been observed or even expected since the temperature can only change the energy slightly. Such a significant frequency shift is due to the orientation change of PIC molecule induced by temperature, leading to the change in the frequency of N≡C bond that directly interacts with the Au surface, as shown in Figure 1A. We then construct a working curve of temperature with frequency, which shows a very good linear relationship and can be used to measure the surface temperature of Au NP substrates. A high sensitivity of 0.232 cm-1/ºC (with an accuracy of 0.43 ºC) is achieved. We then apply this method to probe the laser heating effect of Au NPs on CO adsorption and desorption and the local temperature change of single living cells during physiological processes.

EXPERIMENTAL SECTION Sample preparation. SERS substrate preparation was started by synthesizing the Au NPs through the seed-mediated growth method.41 Au seeds with a diameter of 35 nm were prepared by reduction of HAuCl4 with sodium citrate in an aqueous solution according to the Frens’ method.42 Further growth of the seeds to monodisperse 55~60 nm Au NPs was realized by adding HONH3Cl (25 mM, 30 ml) into the 50 mL 35 nm Au sol (~1.4×1011 NPs/ml) while stirring, followed by the addition of HAuCl4 (2.5 mM, 30 ml) into the above solution under stirring at room temperature for several minutes. Cover glass were cleaned with the piranha solution (mixture of H2SO4 + H2O2 = 3:1 (v/v)) for 1 hr, and followed by thoroughly rinsing with ultrapure water. ITO glass were cleaned with acetone (30min sonication), isopropanol (30min sonication) and ultrapure water (10min sonication, twice). The cover glass or ITO glass were then soaked in 0.2% (3-aminopropyl) trimethoxysilane for 12 hrs, followed by thoroughly rinsing with ultrapure water and blowing to dry with N2. The glass was

then baked in oven at 110 °C for 30 min to remove the physisorbed molecules. Finally, the glass was immersed into the Au colloidal solution for 24 hrs to obtain the immobilized Au SERS substrate. For preparing the temperature sensing substrate, the SERS substrate was soaked into 10-3 M PIC ethanolic solution for 30 min, followed by rinsing with copious amount of ethanol to remove physisorbed PIC and dry in air. For preparing PIC modified Au NPs, 10 µl of 1 µM HS-PEG aqueous solution was added into 1 ml of as-prepared Au colloidal solution (with a diameter of 55~60 nm). The mixture was then sonicated for 10 s, followed by 10 min static standing. Then 10 µl of the 10-4 M PIC ethanolic solution was added into the above solution, followed by 10 s sonication and 10 min static standing. The solution was then centrifuged and the supernatant was removed. The residual was then re-dispersed for further use. Raman measurements. Raman measurements in the present work were mainly performed on a home-modified Invia confocal Raman microscope (Renishaw, UK) with dual microscopes, upright (Leica DM2500) and inverted (Leica DMI3000B) microscopes for different samples. The Raman system is equipped with three wavelengths, 532, 633, and 785 nm. The edge filters were used to reject the laser light and Rayleigh scattering at the excitation wavelength. The focal length of the monochromator is 250 mm. In the present study, we used 633 nm as the excitation laser, and an 1800 g/mm grating to achieve the highest spectral resolution. The microscope objective is of 50× magnification with a numerical aperture of 0.55, resulting in a laser spot size of about 1 µm. The temperature and laser power dependent experiments were carried out on the upright microscope. If not otherwise specified, the laser power was 2.67 µW and the acquisition time was 10 s for the experiments carried out in air. The experiments related to living cells in liquids were acquired on the inverted microscope. Due to the fast dissipation of the heat, the laser power used in the liquid phase study can be higher. Usually the laser power was 26.7 µW, and the acquisition time was 5 s.

RESULTS AND DICUSSION Temperature Sensing Using the Frequency Shift of N≡ ≡C Stretching Vibration. In order to check the possibility of using the frequency shift of PIC for temperature sensing, we


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Figure 2. Laser-induced desorption of carbon monoxide (CO) on the Au surface. (A) Schematic of temperature induced CO desorption from Au NPs surface; (B) Temperature (from 1 to 6) and (C) laser power (from 7 to 11) dependent SERS spectra of CO in the spectral range of C≡O stretching vibration. The electrolyte was 0.1 M NaClO4.

investigate the temperature-dependent SERS behavior of PIC adsorbed on the Au NP surface on an in-situ temperaturecontrolled Raman cell (see Figure S1 for details). The sample was prepared by immersing a Au NP-modified cover glass into the PIC solution (see experimental section for sample preparation) for 30 minutes, followed by rinsing with ethanol to fabricate self-assembled monolayer (SAM) molecules on the top of surface, as shown schematically in Figure 1A. The SERS experiment was performed with a very low laser power (2.67 µW) using 633 nm as the excitation source to avoid the heating effect of the laser (see SI-1). Figure 1B shows temperature-dependent SERS spectra of PIC in the N≡C stretching vibration region. For clarity, the peak position, the full width at half maximum (FWHM), and the intensity are plotted as a function of the temperature (Figure 1D). It is interesting to find that the peak intensity keeps almost constant at temperatures lower than 100 ºC but starts to decrease above this temperature and becomes barely detectable at 140 ºC (see Figure S3). It may be due to either desorption of the molecules from the surface or destroy of the SERS substrate. In fact, SEM image or SERS spectra of the substrate after being heated up above 140 ºC reveals that some Au NPs coalescence, which leads to the decrease of the SERS signal (see SI-2). The peak position and FWHM shows a very good linear dependence with temperature at temperatures lower than 100 ºC, both of which can be used as indicators of the temperature. As it is more convenient to determine the peak position than the FWHM, we use only the peak position in this work. The temperature coefficient of the peak position is about 0.232 cm-1/ºC determined from the slope of Figure 1D, which is about 10 times higher than that using the frequency shift in carbon nanotube or silicon cases (0.0288 cm-1/ºC, as reported in literature as well as our own study, see SI-3). The slope indicates the sensitivity of this temperature sensor is about 0.43 ºC, on the basis of the 0.1 cm-1 accuracy in determining the peak position by fitting the Raman spectrum. Such an improvement of the sensitivity is highly important for probing the small temperature variation, especially during the physiological processes of living cells. Although such a temperature dependent peak position change looks similar to that of potential dependent peak shift, in which an electrochemical Stark slope of 25 cm-1/V was

found.43 However, the energy difference as a result of the change of temperature (kBT) can be negligible in comparison with the change of the potential. Therefore, it is unusual to observe such a significant frequency shift with temperature. A recent theoretical calculation for 1, 4-phenylenediisocyanide (PDI) adsorbed on a Au (111) surface revealed that the PDI molecule might take different orientations on the surface.44 The adsorption energy was found to differ by less than 50 meV for five different tilted angles, which implies that these configurations may coexist at room temperature, with the more tilted orientation having a weaker interaction with the Au surface and lower N≡C stretching frequency.44 At a low temperature, most PIC molecules are adsorbed on the surface with a more vertical orientation (inset in Figure 1A, bottom), in which an effective donation of the electron in the antibonding orbital to metal leads to an increase of the bonding strength of the N≡C bond. As a result, the frequency is located at a much higher frequency about 2200 cm-1 compared with the 2130 cm-1 of the free PIC molecule.45,46 However, with the increase of the temperature, more molecules take the tilted orientation (Figure 1A, insert graph, θ1 < θ2 < θ3 < θ4), in which the donation becomes weaker, leading to a weaker N≡ C bond and a lower frequency. Meanwhile, a larger FWHM indicates that more molecules with different tilted angles coexist on the surface. At a temperature higher that 100 ºC, some molecules may be desorbed, evidenced by the decreased peak intensity and a further red shift of the Raman peak. In addition, the largest red shift of our result is about 30 cm-1 falling within the frequency difference for various titled configurations.44 It should be noted that in the low temperature range, such a temperature dependent behaviour is highly reversible, and the frequency of the N≡C bond is insensitive to its surface coverage and is only slightly influenced by the surface facet structure of Au NPs (e.g., Au nanocube and Au octahedron NPs). These facts further proves the frequency change is not due to the desorption-induced surface coverage change, chemical reaction, or different adsorption sites (see SI-4 and SI-5 for detailed discussion). Such a temperature dependent frequency shift of the N≡C vibration of PIC can be developed a unique temperature measuring method by using Figure 1D as the working curve with



the experimentally detected N≡C vibration frequency. Since the PIC molecules are directly adsorbed on the NP surface, they feel the surface temperature of the Au NPs, which is more accurate in evaluating thermoplasmonic effect on the surface where the reaction occurs than the existing methods that can only measure the average temperature in the bulk. For this purpose, we estimate the local temperature by detecting the N ≡C vibration frequency shift under the illumination of different laser powers (see Figure 1C for some representative spectra). It is clear that the peak position red shifts with the increased laser power, which can be more clearly seen from the plot of the peak position against the laser power (Figure 1E). With the measured frequency, we can estimate the temperature using the working curve shown in Figure 1D. With the increase of the laser power from 4.6 µW, the substrate temperature starts to increase almost linearly with the laser power up to 0.1 mW. Then with the further increase of the laser power, the temperature increases at a much lower slope than that at the low laser power. We propose that, at the laser power above 0.1 mW (the turning point of the curve in Figure 1E), the substrate temperature is significantly higher than that of the environment and the heat generated in the NPs may quickly dissipate into the surrounding environment. Therefore, the laser heating effect deviates from the linear response. From Figure S9, we can find that the SERS intensity deviates from the linear response at 0.52 mW, indicating damage of substrate and desorption of some molecules from surface (see SI-2), which leads to the decrease of the SERS intensity. According to the frequency, we can calculate from the working curve that the temperature is about 65.7 ºC, which is lower than the case of the temperature dependent study. We propose the difference is due to the fact that in the laser heating case, the SERS signal obtained is an average temperature of the NPs’ hot spots in the laser spot. The spot producing the high SERS enhancement may not be the spot generating the most efficient heating effect.47 At a laser power of 0.9 mW, we observed a significant broadening of the Raman peak, indicating a serious damage of both substrate and molecules, as in the case of high temperature in the temperature-dependent study. This result also implies that in the SERS measurement the laser power should be well controlled to avoid its interference to or even damage of the sample, which has been frequently observed in SERS literatures, and to obtain reproducible and reliable SERS spectra for the practical SERS application. CO Photothermal Desorption from Au NPs Surface. To further prove the reliability of our method, we applied it to investigate the weak interaction system of laser-induced desorption of carbon monoxide (CO) on the Au surface. CO is a profound poison species in the heterogeneous catalysis and photoelectrochemical reaction, it is of both fundamental and technological importance to accurately measure its desorption temperature at metal surface during the photothermal process. By controlling a negative potential of -0.8 V (vs SCE) of the Au NPs assembled ITO electrode, CO can be adsorbed strongly on the Au surface to ensure the detectable SERS signal, as shown in Figure 2A (bottom one). The laser power was controlled at 25 µW, which will not induce notable heating effect in the aqueous solution (see SI-6). At room temperature (22 ºC), no apparent peaks could be observed in the region of 1900 cm-1 to 2300 cm-1 in the electrolyte without CO (Figure 2B, NO. 1), whereas a new peak appeared at 2106 cm-1 related to C≡O stretching vibration of the adsorbed CO molecule on Au surface (Figure 2B, NO. 2) in CO saturated 0.1 M NaClO4

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solution. The peak intensity almost did not change at the temperature of 32 ºC, 42 ºC and 52 ºC (Figure 2B, NO. 3, 4, 5). However, when the temperature was raised to 62 ºC, the peak totally disappeared (Figure 2B, NO. 6), indicating desorption of CO from the surface (see Figure 2A, top). Therefore, a temperature of 62 ºC is higher enough to break the Au-CO bond. Upon cooling the temperature back to 22 ºC and replacing the electrolyte with fresh CO saturated 0.1 M NaClO4 solution, the peak recovers with the same frequency and almost the same intensity (Figure 2C, NO. 7) at the same sample spot, indicating the heating experiments have not damaged the Au NPs. By using PIC adsorbed Au NPs substrate, we made a working curve in the 0.1 M NaClO4 solution (see Figure S10A), showing a slightly lower sensitivity of 0.193 cm-1/ºC, with which we can measure the temperature at different laser powers (shown in Figure 2C). The laser power dependent SERS spectra are shown in Figure 2C, from which the CO peak is visible when the power is lower than 301 µW (corresponding to 51.5 ºC, see Figure S10B), agreeing with the temperature dependent result shown in Figure 2B. At a laser power of 690 µW corresponding to 61.3 ºC, the CO signal disappeared (Figure 2C, NO. 11), agreeing well with the desorption temperature of 62 ºC in Figure 2B. This study strongly demonstrates the accuracy of our method. We did observe a small signal loss at the laser power of 301 µW corresponding to a temperature lower than the desorption temperature of CO (Figure 2B, NO. 5). Such a phenomenon may be attributed to the light-assisted oxidation of CO molecules under the high laser power.48

Figure 3. Temperature mapping of single living cell under different culture temperature. (A) The white light image of a living CaSki cell on the temperature sensing substrate. Temperature mapping of the cell at different culture temperatures: (B) 27, (C) 32, (D) 37, and (E) 40 ºC.

Single Living Cell Temperature Mapping under Different Culture Temperature. The above results demonstrate the reliability of this SERS frequency shift based method and it can well be applied to aqueous solution. It would be intriguing if this method can be further extended into more demanding single living cell thermometry that requires a high spatial resolution. The temperature of a single living cell is vitally important to the chemical and biological processes of the cell, including the enzymatic reaction, gene expression and intermolecular reaction.25 It is known that the cell temperature of some malfunctioned cells will be higher than that the normal cells because of the faster metabolism. The cell temperature can be used as an important indicator of some diseases. If the


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Figure 4. Temperature sensing of single living cell during active Ca2+ transport. (A) Experimental scheme; (B) The dependence of N≡C peak position on the time before and after injection of potassium ion.

same PIC-adsorbed substrate is used and to be immersed in the cell medium, the PIC molecules will be quickly replaced by the biomolecule in the culture medium, leading to the disappearance of the PIC signal. To solve this problem as well as to avoid the sensitivity decrease in the liquid environment (see SI-6), we first modified the immobilized Au NPs with biocompatible PEG-SH (3000 Da). The PIC molecules were allowed to be adsorbed on the Au surface in root of the PEG molecules. Such a modification significantly improves the stability of the substrate and PIC signal. More importantly, due to the protection of the PEG layer, the slope of working curve obtained in the cell culture medium is 0.236 cm-1/ºC, which is in good agreement with the 0.232 cm-1/ ºC in air (see SI-7). Therefore, we can measure a SERS spectrum at room temperature first to calibrate the working curve for temperature sensing. We then measured the cold resistance of single living CaSki cell in the temperature-controlled in-situ Raman cell. Figure 3A gives the white light image of the cell. Figure 3 (B to E) gives the temperature mapping using the frequency shift for the four temperatures, from which we can clearly see the cell contour. At a low temperature (27 ºC, Figure 3B), there is an obvious temperature difference (about 7 ºC) between the substrate without and with cell. With the increase of the temperature, the temperature difference becomes 6, 4, and 2 °C for the controlled temperature of 32, 37, and 40 °C, respectively. It indicates that the cell may accelerate the metabolism in order to maintain physiological temperature at a low temperature. However, when the temperature was controlled at 40 ºC (Figure 3E), we observed an increase of the temperature of the cell. It is highly possible that the disorder of physiological control system of the cell at such a high temperature leads to a higher temperature in the region having cells, which needs further investigation. This result indicates the cell can adjust its metabolic process to keep the temperature under its physiological benign condition to handle the stress induced by the environmental temperature change. Local Temperature Variation of Single Living Cell during Active Ca2+ Transport. The above study only demonstrated the use of SERS substrate to monitor the surface temperature, including the extracellular temperature. In fact, in practical applications, it is more important and challenging to monitor the intracellular temperature or the temperature in the solution. Here, our method can be easily converted to be a general nanothermometer by modifying Au NPs with PIC for probing the temperature evolution during the active transport of the calcium ion into cell.49 To obtain the temperature sensing colloids, we first modified the Au NPs with PEG-SH, and

then PIC. Then the Au NPs were incubated together with CaSki cells for 4 hrs. The scheme for such kind of experiment was given in Figure 4A. We first added 1 ml of 1mM CaCl2 solution into the culture medium. Then we used a micromanipulator to control the approaching of a micropipette to the cell to release 20 µl of 60 µM potassium ion, which will trigger transportation of the calcium ion to the target cell. The temperature of the injected solution and the culture medium were kept the same to avoid the disturbance of the local temperature during injection. Due to the necessity of introducing the micropipette, the experiment could only be done at the ambient temperature in the current setup. It can be seen from Figure 4B that, before the injection of the solution, the cell temperature remains almost constant. After the injection of the potassium ion, the cell temperature slowly rises and reaches the highest temperature difference of 7.6 ºC in 10 min. Then the temperature slowly returns to the environment temperature. The absolute SERS signal intensity in small aggregate systems was much weaker than that on the assemble substrates, which leads to a low signal to noise ratio in SERS spectra (see Figure S12). Therefore, we would expect a large error in fitting the peak position and in detecting the temperature. However, the large amount of data can still produce sufficiently good statistic to show the temperature change in Figure 4B, which proves that this method is adequate to retain the high sensitivity in monitoring the intracellular temperature. Taken together, the above two systems demonstrate the capability of the present method for tracking the local temperature of single living cell.

CONCLUSIONS In summary, we proposed a method of using PIC molecule adsorbed on Au NPs for the local temperature sensing. The PIC molecule will take more tilted angle to the Au surface with the elevation of the temperature. As a result, the donation of the anti-bonding electron of the N≡C bond weakens, leading to the weakening of the N≡C bond and red shift of the N ≡C stretching frequency. We observed a good linear relationship between the temperature and N ≡ C frequency, which forms the basis of using it as a temperature sensing indicator. We then demonstrated the temperature sensing capability for measuring laser heating effect of a Au NP immobilized substrate in both air and liquid state. We found that the temperature could be easily elevated up to 65.7 ºC with a laser power of 0.52 mW in the air, which points to the importance of controlling the laser power density to avoid the disturbance of the system to be measured in practical SERS measurement, especially when Au NPs are to be used as substrates. In the liquid



environment, we probe the temperature induced desorption of CO from Au NPs surface. Impressively, our method gave an accurate desorption temperature compares with that measured by thermocouple, which strongly demonstrates the reliability of our method. Furthermore, the developed method was successfully applied for measuring the extracellular and intracellular temperature during physiological processes of single living cell. The virtue of the present SERS-based method is that the measured temperature is right at the very surface of the NPs, which can effectively overcome the averaging effect while measuring the bulk species. Therefore, it will provide a much accurate way to measure the local temperature for a wider application.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. SI-1. Selection of proper laser power to minimize the influence of the laser heating effect SI-2. Influence of the substrate temperature on the substrate morphology and molecule adsorption SI-3. Temperature sensing using the peak shift of silicon single crystal and single-walled carbon nanotube (SWNT) SI-4. The effect of coverage on the peak position SI-5. The effect of surface facet on the peak position of N≡C SI-6. Working curve and laser heating effect in 0.1 M NaClO4 aqueous solution SI-7. Working curve obtained in the cell culture medium Figure S1. A home-designed Raman cell used for the temperature dependent study Figure S2. Optimization of detecting conditions for the local temperature sensing Figure S3. The peak area of the N≡C peak as a function of temperature Figure S4. The SERS signal of the heated substrate (110 °C and 140 °C) cooled to normal temperature (27 °C) and reabsorbing PIC Figure S5. The SEM images of SERS substrate before and after heated to 140 °C Figure S6. The temperature dependent Raman spectra of silicon and single-walled carbon nanotube Figure S7. The dependence of the N≡C peak position of PIC molecule on the surface coverage Figure S8. The dependence of the peak position of N≡C of PIC on different crystal facets Figure S9. Laser power-dependent intensity of the N≡C stretching vibration of PIC adsorbed on Au NPs Figure S10. Temperature and laser power dependent frequency shift of N≡C peak in the electrolyte of 0.1 M NaClO4 Figure S11. The working curve of temperature dependent frequency shift in the cell culture medium Figure S12. SERS spectra of PIC molecules adsorbed on Au NP colloids and assembled substrate

AUTHOR INFORMATION Corresponding Author * [email protected]

Author Contributions † These authors contributed equally.

Notes

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ACKNOWLEDGMENT We thank Dr. Hai-Xin Lin for helpful discussion. We acknowledge support from the National Natural Science Foundation of China (21633005, 21790354, 21711530704 and 21621091) and the Ministry of Science and Technology of China (2016YFA0200601 and 2013CB933703) others for any contributions.

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The authors declare no competing financial interests.


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Table of Contents (TOC)



Figure 1. Temperature sensing using PIC molecules adsorbed on Au NPs surface. (A) Schematic of temperature-dependent SERS measure-ment and temperature induced orientation change of PIC molecules. (B) Temperature and (C) laser power dependent SERS spectra of PIC in the spectral range of the N≡C stretching vibration; (D) Raman shift and FWHM of the N≡C peak as a function of temperature. (E) Raman shift of the N≡C peak as a function of laser power. The laser power used in (B) was 2.67 µW. 177x51mm (300 x 300 DPI)


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Figure 2. Laser-induced desorption of carbon monoxide (CO) on the Au surface. (A) Schematic of temperature induced CO desorption from Au NPs surface; (B) Temperature (from 1 to 6) and (C) laser power (from 7 to 11) dependent SERS spectra of CO in the spectral range of C≡O stretching vibration. The electrolyte was 0.1 M NaClO4. 160x63mm (300 x 300 DPI)



Figure 3. Temperature mapping of single living cell under different culture temperature. (A) The white light image of a living CaSki cell on the temperature sensing substrate. Temperature mapping of the cell at different culture temperatures: (B) 27, (C) 32, (D) 37, and (E) 40 ºC. 77x61mm (300 x 300 DPI)


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Figure 4. Temperature sensing of single living cell during active Ca2+ transport. (A) Experimental scheme; (B) The dependence of N≡C peak position on the time before and after injection of potassium ion. 140x49mm (300 x 300 DPI)



Table of Contents (TOC) 80x53mm (300 x 300 DPI)


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Quantifying Surface Temperature of Thermoplasmonic Nanostructures

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