Polydopamine-mediated gold nanoparticle coating strategy and its application in photothermal polymerase chain reaction

Abstract

Materials with high light-to-heat conversion efficiencies offer valuable strategies for remote heating. These materials find wide applications in photothermal therapy, water distillation, and gene delivery. In this study, we investigated a universal coating method to impart photothermal features to various surfaces. Polydopamine, a well-known adhesive material inspired by mussels, served as an intermediate layer to anchor polyethyleneimine and capture gold nanoparticles. Subsequently, the coated surface underwent electroless gold deposition to improve photothermal heating efficiency by increasing light absorption. This process was analyzed through scanning electron microscopic imaging and absorbance measurements. To demonstrate functionality, the coated surface was photothermally heated using a light-emitting diode controlled with a microprocessor, targeting the metal regulatory transcription factor 1 gene—a marker for osteoarthritis—and the S gene of the severe fever with thrombocytopenia syndrome virus. Successful amplification of the target genes was confirmed after 34 polymerase chain reaction cycles in just 12 min, verified by gel electrophoresis, demonstrating its diagnostic applicability. Overall, this simple photothermal coating method provides versatile utility, and is applicable to diverse surfaces such as membranes, tissue culture dishes, and microfluidic systems.

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Introduction

As implied by their name, photothermal materials possess a strong capability to absorb and convert light into thermal energy.^1,2 Activated by incident light, these materials can be integrated into systems that are unable to connect directly to an electric circuit (e.g., living organisms) or utilized to harness solar energy for heat generation.^3–7 Therefore, these materials have been extensively discovered in nature or synthesized for applications in photothermal therapy,^4,8 light-triggered drug delivery,^9,10 soft robotic actuation,^5,11 and water distillation.^6,7 Notably, photothermal materials that effectively convert near-infrared (NIR) light into thermal energy are particularly valuable for in vivo biomedical applications. NIR light, with wavelengths in the range of 750–1350 nm, exhibits low tissue absorption and allows deep tissue penetration.¹² Materials exhibiting high photothermal efficiency can be classified into various types, including plasmonic nanoparticles, semiconductors, carbon-based nanomaterials, and polymers.^1,13–15 Among these, plasmonic nanoparticles, particularly gold nanoparticles (AuNPs), are extensively used in photothermal applications owing to their ability to finely tune absorption wavelengths, high photothermal conversion efficiency, facile surface modification, and biocompatibility. Depending on their size and aspect ratio, AuNPs can exhibit absorption peaks ranging from 520 nm to the NIR region. Therefore, various gold nanostructures such as nanospheres, nanorods, nanostars, nanocubes, and nanofilms have been used to efficiently convert light into heat.^16–21 Although colloidal nanoparticles are widely used in biomedical applications, immobilizing photothermal agents on surfaces becomes necessary for specific applications. These applications include light-triggered robotic actuation,^5,11,22 water treatment using photothermal membranes,^6,7 and antibacterial surfaces.¹⁸ Photothermal materials have also been extensively utilized in polymerase chain reactions (PCRs) because of their rapid heating capabilities. Rapid heating and cooling of PCR reagents are crucial for reducing overall reaction times. In photothermal PCR, heating can be achieved using two primary methods: volumetric heating and thin-film heating. In volumetric heating, colloidal AuNPs are often mixed with PCR reagents to uniformly heat the entire solution. However, challenges arise when highly concentrated nanoparticles are used, such as potential PCR inhibition due to adsorption or separation of nanoparticles from the amplicons after the reaction.^23,24 Thin-film heating has gained prominence in recent years, where nanometer to micrometer-thick layers of photothermal materials rapidly diffuse heat for efficient heating and cooling, compared to traditional bulky PCR cycling systems. In one instance, Son et al. deposited a gold nanofilm on polymethylmethacrylate wells using electron beam evaporation to enable ultrafast PCRs controlled using light-emitting diodes (LEDs). They achieved 30 thermal cycles between 55 °C and 95 °C in just 5 min.²⁵ In another study, a gold layer was deposited on a membrane and soaked with PCR reagents, which were heated using a 785 nm laser, achieving 25 cycles between 63 °C and 96 °C in 12 min.²⁶ To enhance heating efficiency, Jeong et al. developed a nanoplasmonic pillar array with glass pillars coated with gold nanoislands. This substrate exhibited broad absorption across visible light regions and demonstrated excellent photothermal efficiency under white-light LEDs.^27–29 However, the gold layers in these studies were fabricated using physical deposition techniques such as thermal evaporation or electron beam evaporation, which require expensive equipment.

Polydopamine (PDA), a mussel-inspired material, has been developed for a multifunctional coating with exceptional properties, including easy functionalization via Michael addition or Schiff base reactions, metal-reducing capabilities, biocompatibility, and high photothermal efficiency.^30–33 Importantly, PDA allows for a universal coating of nearly any surface by simple immersion in its monomeric solution under alkaline conditions. This characteristic makes PDA an excellent choice for customizing surfaces with diverse chemical functionalities such as bioactivity, antifouling properties, and metal incorporation, independent of surface chemistry.^30,34–40 These versatile features also enable PDA to be combined with other photothermal agents, such as (reduced) graphene oxide, carbon nanotubes, quantum dots, and metal nanoparticles, to attain enhanced heating efficiency.^41–44

In this study, we employed PDA as an intermediate layer to immobilize and develop metal nanoparticles for enabling photothermal heating of surfaces. The surface charge of the PDA film on the target substrate was tuned by conjugating with polyelectrolytes to immobilize the metal nanoparticles. AuNPs, immobilized using this approach, were further enhanced by electroless deposition of gold to increase heating efficiency through enhanced light absorption under LED irradiation. Due to the ability of PDA to uniformly coat surfaces, various substrates can be customized to acquire photothermal properties using wet chemistry-based processes, thereby circumventing the need for costly physical gold deposition methods. To evaluate this approach, we amplified a 171 bp DNA target from the metal regulatory transcription factor 1 (MTF-1) template and the RNA target of the S gene of the severe fever with thrombocytopenia syndrome virus (SFTSV) using PCR or reverse transcription-PCR (RT-PCR) on a photothermal heating platform, where temperature was regulated with a white-light LED.

Materials and methods

Materials

Dopamine hydrochloride, polyethyleneimine (PEI) and gold chloride trihydrate were obtained from Sigma-Aldrich (USA) and Tris-HCl buffer from Biosesang (Korea). Sylgard 184 polydimethylsiloxane was purchased from Dow Corning (NY, USA). Polycarbonate (PC) was purchased from Goodfellow (USA). MTF1 plasmid DNA (HG15046-G) was obtained from Sino Biological (China). The S gene of SFTSV was synthesized by Macrogen (Korea) and transfected into HEK293T cells to produce the lentivirus. Thumb Taq DNA polymerase and a OneStep RT-PCR kit were obtained from BioFACT (Korea).

PDA-mediated metal nanoparticle immobilization

The PDA-mediated photothermal coating procedure is shown in Fig. 1a. First, the surface of interest was immersed in a dopamine hydrochloride (2 mg mL⁻¹) solution in Tris-HCl buffer (10 mM, pH 8) for 12 h and then washed with deionized (DI) water. The PDA-coated surface was subsequently placed in an aqueous PEI solution (0.4 mg mL⁻¹) and heated on an 80 °C hot plate for 30 min. The PDA/PEI-coated substrate was thoroughly washed with DI water to remove unbound PEI. AuNPs were synthesized following the Turkevich method, in which an aqueous solution of gold chloride trihydrate (0.167 mM) was heated with magnetic stirring, followed by the addition of sodium citrate (2.2 mM). After the solution developed a red color, it was cooled to room temperature. The PDA/PEI-coated substrate was then immersed in the AuNP solution for 5 h, causing the substrate to turn red due to the immobilization of negatively charged citrate-capped AuNPs on the amine-rich PEI. To enhance photothermal heating efficiency, the immobilized AuNPs were further subjected to an electroless gold deposition solution comprising varying concentrations (0.5, 1, 2, and 4 mM) of HAuCl₄ with 0.5 M H₂O₂ for 10 min.⁴⁵

Fig. 1 Schematics of (a) PDA-mediated gold coating and (b) on-chip photothermal PCR procedures.

Surface characterization

Scanning electron microscopy (SEM). 5 × 5 mm² PC substrates were coated with PDA/PEI and AuNPs (PDA/PEI/AuNP), followed by electroless gold deposition at various Au³⁺ concentrations (PDA/PEI/AuNP/ELD). The coated PC substrates were then sputtered with Pt using an ion-sputter coater (Hitachi E-1030) and imaged with a SEM (Hitachi SU8600) at an acceleration voltage of 2 kV.

Absorbance measurement. A 96-well plate was directly coated with PDA, PDA/PEI, or PDA/PEI/AuNP, and PDA/PEI/AuNP/ELD. After washing, the absorbance of the coated wells was measured using a microplate spectrophotometer (BioTek Instruments, Epoch™) after adding 100 μL of water to each well.

Photothermal heating and temperature measurement

Photothermal heating of the coated surfaces was conducted using a 4000 K white-light LED (Luxeon 7070, L170-4070701200000, Lumileds) placed under the coated substrate. The temperature was measured with an IR camera (FLIR Thermovision A320) and analysed using ThermoCam Quick Plot software. Thermal cycling between denaturation, annealing, and extension temperatures was controlled by connecting the LED to an Arduino Uno, which controlled the LED light intensity and a fan for effective cooling. A thermocouple attached to the reference surface provided temperature feedback to the Arduino, enabling precise LED control.

LED-controlled PCR on chip

To fabricate the photothermal heater for the PCR chip, a PDMS slab was first coated with an optimized PDA/PEI/AuNP/ELD coating (denoted as PDA/gold) following the steps described above. The PDMS slab was then pressed onto double-sided acrylic thermal tape to transfer the PDA/gold layer to the tape, which was subsequently removed, as shown in Fig. 1b. The PCR chip was fabricated using a computer numerical control (CNC) machine to engrave a chamber (d = 6 mm, h = 0.3 mm) on a 0.5 mm-thick PC sheet. After creating the inlet and outlet on each side of the chamber, the engraved PC sheet was thermally bonded to a flat PC sheet (0.5 mm thick) via hot embossing at 135 °C for 10 min. The PDA/gold side of the thermal tape was covered with a thin PC film to prevent dust from sticking to the tape, while the opposite side was attached to the bottom of the PCR chip with double-sided Kapton tape, with 5 mm aluminum foil placed in between for more uniform heat diffusion. The chamber of the PCR chip was incubated with 0.15% bovine serum albumin (BSA) for 2 h to reduce nonspecific binding of the PCR reagents. After removing the BSA, 8 μL of the PCR mixture was injected into the chamber, and the inlet and outlet were covered with aluminum tape to prevent evaporation. The PCR mixture comprised 10 μL of 2× Thumb Taq PCR master mix (BioFACT), 9.6 μL of water, 0.67 μM of each primer, and the MTF-1 gene containing plasmid as the DNA template. The primer sequences were 5′-GCC TTC CTC ATC TGG AAC TG-3′ (forward) and 5′-TAA CCC TGG GAC ATT GCT TC-3′ (reverse), designed to amplify 171 bp amplicons. After the PCR, the results were confirmed by gel electrophoresis.

To confirm its efficacy against RNA-based viruses, we performed RT-PCR on photothermally heatable PCR chips, targeting the S gene of SFTSV. The OneStep RT-PCR Kit (BioFACT) was used, containing 0.67 μM of each forward and reverse primer, 0.033 U μL⁻¹ of Taq polymerase, and 8 copies per μL of the thermally-lysed target RNA for both on-chip and off-chip reactions. The primer sequences were 5′-TCC CAC TAG GCC ACC TAA G-3′ (forward) and 5′-AGG GAC CTC GTT GAA TGC T-3′ (reverse).

Results and discussion

Surface characterization of PDA/gold coated surfaces

The immobilization and growth of the AuNPs are shown in Fig. 2. PDA can be easily coated onto various substrates and facilitates chemical reactions with amines via Schiff base reactions. PEI is an amine-rich polymer that exhibits a positive charge in the acid–neutral pH range. In this study, PEI was covalently linked to PDA-coated surfaces to electrostatically capture the negatively charged citrate-capped AuNPs. The SEM images in Fig. 2a show the successful immobilization of AuNPs and the growth of gold by electroless deposition. Initially, the PDA/PEI-coated surface shows a smooth morphology (i), but after incubation with the AuNP solution, the presence of nanoparticles (d = 26 ± 2.6 nm) became visible on the PDA/PEI coated surface (ii). Electroless deposition with 0.5 mM Au³⁺ showed only a minor size increment to d = 28 ± 2.5 nm (iii), but increased concentrations of Au³⁺ from 1 to 4 mM resulted in the growth of individual nanoparticle size as well as the coalescence of adjacent nanoparticles (iv–vi). The use of AuNPs as nucleation sites for electroless gold deposition is a well-known technique for chemically developing a thin gold film on a surface. Hu et al. immobilized AuNPs on a glass substrate treated with (3-aminopropyl)trimethoxysilane for electroless gold deposition using only HAuCl₄ and H₂O₂.⁴⁵ By performing electroless gold deposition, the empty spaces between the nanoparticles were reduced, resulting in increased visible-light absorption. As shown in Fig. 2b, after incubation with AuNPs, a peak appeared at approximately 530 nm, indicating the presence of AuNPs on the PDA/PEI surface. This peak gradually red-shifted to 540, 560, and 570 nm after gold electroless deposition with increasing Au³⁺ concentration from 0.5 mM to 2 mM, respectively. Correspondingly, the color shifted from red to blue (Fig. 2c). The gold deposition process also increased the overall absorption at all measured wavelengths, possibly by filling the gaps between the nanoparticles. At 4 mM Au³⁺, the plasmon resonance peak disappeared as the AuNPs coalesced to form a continuous gold film, as evidenced by the typical bulk gold color.

Fig. 2 Surface characterization of PDA/gold-coated surfaces. (a) SEM images showing AuNPs immobilized onto PDA/PEI-coated surfaces under varying conditions of gold electroless deposition: (i) PDA/PEI, (ii) PDA/PEI/AuNP, (iii) PDA/PEI/AuNP/ELD-0.5, (iv) PDA/PEI/AuNP/ELD-1, (v) PDA/PEI/AuNP/ELD-2, and (vi) PDA/PEI/AuNP/ELD-4. Scale bar = 300 nm. (b) Corresponding absorption spectra. (c) Color images of circular PDMS slabs after respective coating procedures. Scale bar = 5 mm. “ELD-X” indicates gold electroless deposition with X mM Au³⁺.

Light-induced heating of the PDA/gold coating

To test the photothermal heating effect of the coating, thermal tapes coated with various coating conditions were attached to a glass slide and irradiated with a white-light LED, as shown in Fig. 3a. The temperature of the coated thermal tape when the LED was turned on for 60 s and off for 60 s was measured using an IR camera, as shown in Fig. 3b, where an elevation in temperature was observed during the “on” state. PDA is widely known as an efficient photothermal material; therefore, PDA/PEI showed a higher temperature increment when compared to bare tape. The temperature of the PDA/PEI-coated thermal tape reached 94 °C, which was 34 °C higher than the bare tape. After immobilizing negatively charged AuNPs onto the PDA/PEI layer, the temperature increased further from 94 °C to 129 °C. The measured temperatures further escalated to 162 °C and 180 °C after gold electroless deposition using 1 mM and 2 mM Au³⁺, respectively. However, when the concentration of Au³⁺ was increased to 4 mM, the temperature did not increase further, with the maximum temperature reaching 177 °C after 60 s of irradiation. Although the overall light absorbance was enhanced by increasing the thickness of the gold layer, the temperature did not increase, presumably because the light-to-heat conversion efficiency decreased with increasing particle size.^46,47 Scattering overshadows absorption when the particle size is large, which can lower heating efficiency.^48,49 Overall, 2 mM Au³⁺ was chosen as the optimal concentration for electroless deposition to develop a gold layer, and this condition was used for further experiments (referred to as “PDA/gold” hereafter). Fig. 3c shows the heating and the cooling rate of PDA/gold for the initial 10 s at different LED powers. Fig. 3d shows the IR images of a 1.5 mL Eppendorf tube without and with the PDA/gold coating. When irradiated with an LED for 5 min, the coated tube heated 250 μL of water more effectively (Fig. 3d).

Fig. 3 Photothermal heating characterization. (a) Graphical representation of photothermal heating for different coatings. (b) Temperature changes of thermal tape with various coating conditions measured using an IR camera. The LED (4 W) was alternated between on (60 s) and off (60 s) during measurements. (c) Heating and cooling rates of PDA/gold at different LED powers. (d) IR camera images showing bare and PDA/gold-coated 1.5 mL tubes containing 250 μL water after 5 min of LED irradiation. (e) Overview of the device setup for PCR thermal cycling, and (f) PCR temperature control steps implemented by the system. (g) Actual image of the thermal cycling device.

Fig. 3e shows an overview of the device setup used for temperature control during thermal cycling. The temperature was measured using a thermocouple placed on the center of 0.5 mm thick PC attached with the PDA/gold coating. According to the temperature data obtained from the thermocouple, the Arduino controls the white-light LED and fan to heat and cool the surface, respectively. Using this setup, the temperature was either elevated or lowered and kept at predetermined temperatures as shown in Fig. 3f. This result demonstrates that precise temperature control is possible using this system. The actual image of the setup can be found in Fig. 3g.

Photothermal amplification of target DNA

Using the system described above, on-chip PCR was performed using an LED for thermal cycling. First, the PCR mixture was introduced into the chip, and the inlet and outlet were tightly sealed using aluminum tape. The PCR chip was attached to double-sided thermal tape coated with PDA/gold, with aluminum foil on each side, as shown in Fig. 1b and 4a. The LED light directly irradiated the PDA/gold to heat the PCR mixture inside the chip. Fig. 4b shows the result of the evaporation test after 34 thermal cycles. 8 μL of water was added into the PCR chip and collected for volume measurement after 34 thermal cycles. The result showed that a water loss of approximately 0.38 μL was observed on average when thermal cycling was not performed. This means that on average, 0.38 μL of water was lost by adsorption on the chip. When thermal cycling was performed, the water loss was increased to approximately 0.68 μL, which means on average, 0.3 μL of water was lost by evaporation. Approximately 3.8% of water was lost during 34 cycles of PCR indicating that the thermally bonded chip and sealing tape effectively prevented evaporation of the reaction solution during the photothermal PCR process.

Fig. 4 Photothermal PCR on chip. (a) Schematics of photothermal PCR on chip, with temperature controlled with an LED using data from a thermocouple. (b) Results of the evaporation test performed. 8 μL of water was added into the PCR chip and collected with or without 34 thermal cycles and the volume was measured. (c) Results of agarose gel electrophoresis of on-chip reactions: 171 bp target amplicons from the MTF-1 gene, displaying varying denaturation temperatures on the reference surface (left) and triplicated reactions with optimized denaturation temperature (right). (d) Actual temperature profile during thermal cycling, measured using an IR camera. (e) Gel electrophoresis result of two-step benchtop and photothermal PCR when different concentrations of MTF-1 plasmids were used. 1–4: Benchtop PCR thermocycler (5, 0.5, 0.05, and 0.005 pg μL⁻¹, respectively) and 5–8: photothermal PCR device (5, 0.5, and 0.05 pg μL⁻¹, respectively).

Accurate temperature control during PCR is crucial for achieving highly efficient DNA amplification. Measuring the exterior temperature of a PCR chip may not accurately reflect the temperature of the solution inside. Therefore, we connected two LEDs in parallel and placed only the lower substrate (0.5 mm thick PC) of the PCR chip above one LED to measure its temperature for reference. The complete PCR chip, containing a PCR reagent solution with MTF-1 plasmids, was placed above the other LED to conduct the reaction. By testing different denaturation temperatures, we determined the optimal temperature for successful PCR. Among the various temperatures tested, only a denaturation temperature of 102 °C exhibited a clear band, confirming that achieving PCR on a complete PCR chip requires elevated temperatures due to the added heat capacity from the reagents and the upper substrate of the PCR chip (Fig. 4c). Accurately measuring the temperature of a small system is a challenging task, but it has been achieved by other researchers through methods such as placing a reference reaction chip in parallel⁵⁰ or embedding a resistance temperature detector on the photothermal heater.²⁹ Based on this information, photothermal amplification of the target plasmids was repeated thrice, and each run showed clear bands at 171 bp, indicating successful PCR. LED-driven thermal cycling was performed 34 times within 12 min (Fig. 4d).

Fig. 4e shows that the introduced microdevice successfully amplified the target DNA template as low as 0.5 pg μL⁻¹. As shown in the gel image, although the on-chip amplification showed weaker band intensity compared to the off-chip reaction, it still displayed a clear single band which indicated successful amplification. The difference in the intensity could be due to the difference in the PCR mixture volume. As for the off-chip reaction, a higher volume was used (20 μL) compared to that used for the on-chip reaction (8 μL). Despite BSA being coated on the surface of the PCR chamber, the high surface area to volume ratio of the chamber could have increased the non-specific adsorption, inhibiting the reaction.

Photothermal RT-PCR of target RNA

To demonstrate the platform's capability for detecting RNA viruses, the S gene of SFTSV was amplified using RT-PCR (Fig. 5). Fig. 5a outlines the temperature and time protocol for both on-chip and off-chip reactions, including reverse transcription, initial denaturation, final extension, and 34 thermal cycles. Although the 171 bp amplicon targets from MTF-1 plasmids were successfully amplified with rapid alternation between denaturation and annealing temperatures, the SFTSV target amplicon size was larger (221 bp) and required an extended extension time. Therefore, a 2 s extension step was added to the amplification cycle to complete the reaction. Although two-step PCR is commonly used for rapid PCR, particularly for short amplicons, an additional extension step is necessary for long amplicons due to the limited extension rate of Taq polymerase. The temperature profile during on-chip RT-PCR is shown in Fig. 5b. Following the temperature protocol, clear 221 bp bands appeared in the replicated on-chip reactions, as shown in Fig. 5c.

Fig. 5 Results of photothermal RT-PCR of the synthesized S gene of SFTSV. (a) Protocol depicting the reaction temperature and time for performing RT-PCR of SFTSV. (b) Actual temperature measurements during the reaction recorded using an IR camera. (c) Results of agarose gel electrophoresis comparing on-chip and off-chip reactions, displaying 221 bp amplicons obtained from the S gene of SFTSV.

Conclusions

In this study, we demonstrated a PDA-mediated coating method to endow different surfaces with photothermal features, which we applied to on-chip photothermal PCR. PDA served as an intermediate layer to bind with PEI, enabling the capture of citrate-capped AuNPs via electrostatic interactions. Subsequently, these immobilized nanoparticles were treated by electroless gold deposition to increase their light absorption and improve photothermal efficiency.

Because PDA can be applied to nearly any solid surface, this method is versatile and applicable to various laboratory tools such as PCR tubes, well plates, and coverslips. The PDA/gold layer exhibited excellent heating capabilities upon irradiation with a white-light LED controlled using a microcontroller for heating and cooling the PCR chip. A 171 bp amplicon from MTF-1 was successfully amplified by alternating between denaturation and annealing temperatures, and the results were analyzed by gel electrophoresis. The S gene of SFTSV was amplified using on-chip RT-PCR to demonstrate its applicability to various targets. Although the concept of using photothermal materials for PCR is not new, the main benefit of our method over previous studies lies in the convenience of coating. For example, Son et al. and Lee et al. conducted photothermal PCR by depositing gold thin films using an electron beam evaporator.^25,26 Their results were robust and rapid, establishing the potential use of photothermal materials for biological purposes. Yet, in preparing the gold thin film, they used a physical deposition method such as electron beam evaporation which may not be accessible to many researchers. Hence, the wet chemistry-based coating method can increase the accessibility of making photothermal surfaces without equipment, even in a closed system such as microchambers or microchannels. Moreover, our group previously introduced PDA patterning strategies that can be applied to different types of surfaces.⁵¹ When PDA patterning and nanoparticle immobilization are combined, we believe that they can be utilized for constructing micro- or even nano-sized heaters on various platforms. Heating is triggered solely by light, eliminating the need for direct electrical connections. This capability allows for the implementation of heating systems in environments where direct contact is undesirable, such as cell culture systems or implantable devices. Therefore, we believe that the coating method can be a useful and simple tool for implementing heating apparatuses in various systems.

Comments

Materials with photothermal features can generate heat through light absorption, obviating the need for physical connections like electric circuits. This characteristic has facilitated their use in diverse applications such as photothermal therapy, light-triggered drug delivery, soft robotic actuation, and water distillation. Photothermal materials are particularly advantageous in PCR, where precise temperature cycling (denaturation, annealing, and elongation) is critical. Coating surfaces with nanometer to micrometer-thick layers of photothermal materials enables rapid heating and cooling cycles, significantly reducing overall PCR duration. Therefore, a simple coating strategy to endow various surfaces with photothermal features promises substantial benefits in diagnostics and other light-induced heating applications. In this study, we demonstrate that PDA serves a dual role as a photothermal material and as an intermediate layer for anchoring other photothermal materials onto surfaces. PEI was immobilized on PDA-coated surfaces to bind citrate-capped AuNPs via electrostatic interactions. These nanoparticles were further enhanced through electroless deposition to enhance photothermal heating capabilities. PDA/gold was incorporated into a closed-chamber PCR chip, where alternating heating and cooling cycles of PCR reagents were achieved using a white-light LED, resulting in successful target amplification. Using our system, the MTF-1 and S genes of SFTSV were identified through PCR and RT-PCR, respectively. Specifically, amplification of 171 bp amplicons from the MTF-1 gene was achieved in just 12 min across 34 cycles. Due to its strong adherence to nearly any solid material, PDA can be applied effectively to diverse surfaces. Unlike physical deposition methods, our chemical approach eliminates the need for expensive equipment, broadening its applicability to various settings, including coating inside microfluidic chips. Furthermore, leveraging established PDA patterning techniques, it can facilitate the creation of microheater arrays.

Data availability

All data generated or analysed during this study are included in this published article.

Author contributions

Woo Ri Chae: conceptualization, methodology, investigation, data curation and writing – original draft. Yoon-Jae Song: resources, writing – review & editing. Nae Yoon Lee: conceptualization, resources, project administration, funding acquisition, writing – review & editing, and supervision.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIT) (RS-2023-00208684) and also by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2021R1A6A1A03038996).

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