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Article

Photolithography-Enabled Au/Si Columnar Array Photoelectrochemical Sensor for High-Performance Nitrite Detection

by
Miaotao Li
,
Zhiwei Chen
*,
Zhangcheng Liu
,
Xiao Wang
,
Yang Li
and
Jinping Ao
*
School of Integrated Circuits, Jiangnan University, Wuxi 214122, China
*
Authors to whom correspondence should be addressed.
Materials 2026, 19(5), 921; https://doi.org/10.3390/ma19050921
Submission received: 11 January 2026 / Revised: 2 February 2026 / Accepted: 10 February 2026 / Published: 27 February 2026
(This article belongs to the Special Issue Advanced Applications of Electrochemical Materials for Sensors and Catalysts)
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Abstract

In this work, we demonstrate the fabrication of gold-decorated silicon column array (Au/SiCAs) photoanodes for photoelectrochemical (PEC) nitrite detection. The SiCAs were synthesized on n-type silicon substrates via photolithography and anisotropic etching, after which Au nanoparticles were deposited by magnetron sputtering. The Au/SiCAs photoanodes exhibited a pronounced PEC photocurrent response under the simulated solar irradiation. For nitrite determination, the sensor achieved two broad linear ranges (10–500 μM and 2000–10,000 μM) with corresponding sensitivities of 0.25 and 0.33 μA·μM−1·cm−2, along with a detection limit of 0.25 μM (S/N = 3). Moreover, the sensor exhibited excellent selectivity, remarkable stability, and facile fabrication. Successful detection in real sample confirms its potential for practical applications. This study proposes a novel approach for precise and reliable PEC-based nitrite analysis.

Graphical Abstract

1. Introduction

Nitrites (NO2−) pose potential risks to both the environment and human health [1,2,3,4,5]. From a health perspective, nitrites can easily convert to nitrosamines in the body, which are carcinogenic substances [6,7]. Long-term exposure may lead to respiratory issues and other health risks [8]. Environmentally, nitrites contribute to water eutrophication, potentially causing algal blooms that degrade water quality and disrupt aquatic ecosystems [9]. Therefore, monitoring nitrite levels is crucial. Timely detection and control can effectively reduce health hazards and protect the ecological environment.
So far, many methods have been developed for determining nitrites, including chromatography [10,11], spectrophotometry [12,13], capillary electrophoresis [14,15], fluorescence spectroscopy [16] and chemiluminescence [17,18]. However, these methods often face limitations due to expensive equipment, complex operations, or susceptibility to environmental interference, making accurate and reliable detection challenging. To improve nitrite detection, researchers have explored electrochemical sensors for NO2− [19,20,21,22,23]. Electrochemical methods detect changes in voltage or current resulting from redox reactions of the analyte. They are favored for their high sensitivity, rapid response, portability, and relatively low cost, making them suitable for on-site rapid detection and continuous monitoring [24,25,26]. Among these, photoelectrochemical techniques, a branch of electrochemistry, are widely used in analytical chemistry. By combining optical and electrical signals, photoelectrochemical methods offer higher sensitivity and better selectivity [27,28,29]. Therefore, developing a photoelectrochemical method that can quickly detect nitrites without sample pretreatment or environmental interference is crucial.
In sensing detection, specificity is crucial. Research shows that gold (Au) can serve as a specific film for detection [30,31,32,33,34,35,36,37]. Meanwhile, silicon has excellent photoelectric properties and a mature fabrication process, making it ideal for large-scale production as a sensor material. Therefore, we plan to construct micro–nano structures on a silicon substrate and deposit Au to build photoelectrodes for specific detection [38,39]. Through micro-nano processing technology, we enhance the stability and reproducibility of the samples, ensuring consistent results under different experimental conditions. Additionally, optimizing the micro–nano structures is expected to improve the sensitivity and selectivity of the photoelectrodes, achieving more efficient specific detection.
In this work, we present the preparation, characterization, and performance of a nitrite sensor based on gold-modified microcolumn electrodes fabricated via photolithography and sputtering techniques. Ordered silicon column arrays (SiCAs) were fabricated on the surface of n-type silicon and subsequently functionalized with gold to enable sensitive nitrite detection. The sensor’s performance was evaluated under light illumination using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). As a silicon-based photoelectrochemical sensor, it demonstrated high sensitivity, exceptional stability, and excellent reproducibility in photoelectrochemical measurements, distinguishing it from conventional electrochemical methods.

2. Materials and Methods

2.1. Chemicals and Reagents

Single-side polished n-type silicon wafers (<100> orientation, resistivity less than 10 Ω·cm, thickness approximately 500 μm) were procured from Resemi (Suzhou, China). Sodium nitrite (NaNO2, AR), sodium sulfide nonahydrate (Na2S·9H2O, AR) and anhydrous methanol (CH3OH, GR) were acquired from Titan (Shanghai, China). Anhydrous sodium dihydrogen phosphate (NaH2PO4, AR), anhydrous disodium hydrogen phosphate (Na2HPO4, AR), anhydrous sodium sulfite (Na2SO3, AR), anhydrous sodium sulfate (Na2SO4, AR), ammonium sulfate ((NH4)2SO4, AR), sodium chloride (NaCl, AR), and potassium chloride (KCl, AR) were purchased from Sinopharm (Shanghai, China). Potassium iodide (KI, AR) was purchased from Innochem (Beijing, China). Water nitrite samples were obtained from Meryer (Shanghai, China). The phosphate-buffered solution (PBS) used in the experiments was freshly prepared by mixing NaH2PO4 and Na2HPO4 in deionized water, with a pH of 6.9. All reagents were of analytical grade and employed as received unless otherwise stated.

2.2. Preparation of Photoanode Sensors

The silicon wafers were first diced into pieces measuring 3.5 cm × 3.5 cm using a dicing saw, suitable for subsequent photolithography processes. The diced wafers were then sequentially subjected to ultrasonic cleaning in acetone, isopropanol, and deionized water, with each step lasting 5 min. After cleaning, the wafers were dried under a steady nitrogen stream and annealed on a hot plate to remove any residual solvents. Subsequently, the cleaned wafer is primed via hexamethyldisilazane (HMDS) vapor deposition in an oven, after which a photoresist layer is spin-coated. A soft bake is performed to stabilize the photoresist layer. The pattern is transferred via UV exposure using a mask aligner (MA/BA6, SUSS MicroTEc, Garching, Gemany). Following this, the excess photoresist is removed with a developer, and the wafer is baked again on a hot plate to solidify the photoresist pattern. The silicon wafer with the photoresist pattern is etched using a deep silicon etching system (HSE M200, NAURA, Beijing, China). The cycle of SF6 and C4F8 gases is adjusted to control the etching depth to approximately 100 μm. After etching, the wafer is ultrasonically cleaned sequentially with a stripping solution, acetone, isopropanol, and deionized water, then dried with nitrogen gas. This process yields a silicon wafer with etched column arrays.
For the convenience of subsequent fabrication of sensing electrodes, the silicon wafers with pre-prepared columnar arrays were further sectioned into appropriate dimensions (1.0 cm × 1.7 cm) using a dicing saw, ensuring that a 1.0 cm × 1.0 cm area of ordered silicon columnar arrays remained on the surface. Prior to sputtering, the silicon wafer is cleaned in an HF solution (10 wt%), rinsed with distilled water, and dried with nitrogen gas. Using a magnetron sputtering system (PRO Line PVD 75, Kurt J. Lesker, Jefferson Hills, PA, USA), approximately 40 nm of gold is deposited on the front side of the wafer, while about 300 nm of aluminum [40,41] is deposited on the backside to form an ohmic contact, as shown in Scheme 1. Finally, silicone rubber (Nanda 704) was applied uniformly to all areas of the electrode except the regions in contact with the electrolyte and the electrode holder, using a toothpick as the applicator to ensure precise coverage. This coating served to prevent any contact between the electrolyte and the insulated regions. The electrode was then cured at room temperature for 12 h, yielding the final Au/SiCAs photoanode. The detailed electrode structure is shown in Figure S1. The Si, Au/Si, and SiCAs electrodes are prepared using the same procedure. Figure S2 shows the prepared electrodes.

2.3. Characterization and PEC Detection of Nitrites

The surface morphology of the prepared materials was characterized using a scanning electron microscope (FE-SEM Sigma 300, ZEISS, Oberkochen, Germany). The elemental composition and content were analyzed with an energy-dispersive spectrometer (EDS). UV-Vis diffuse reflectance spectroscopy (DRS) was employed to evaluate the materials’ absorption of UV and visible light. Photoelectrochemical tests were conducted in a three-electrode electrochemical cell, with a platinum sheet serving as the counter electrode and a saturated Ag/AgCl electrode acting as the reference electrode. The tests were performed using a Zennium workstation (Zennium pro, Zahner, Kronach, Germany). All electrochemical characterizations were performed under controlled illumination conditions to evaluate the photoelectrochemical response of the sensor, with illumination provided by a xenon lamp source (PLS-FX300HU, Perfectlight, Beijing, China) at an intensity of 100 mW·cm−2. A 0.1 mol·L−1 phosphate-buffered solution (PBS, pH = 6.9) was used as the electrolyte. Electrochemical impedance spectroscopy (EIS) measurements were conducted in the frequency range of 100 kHz to 100 Hz by applying an AC potential with an amplitude of 10 mV at a potential of 0.6 V. Impedance data were presented as Nyquist plots, and the charge transfer resistance (Rct) values were determined by fitting the data using Zview software (Version 2.70). Linear sweep voltammetry (LSV) was performed at a scan rate of 10 mV·s−1. Cyclic voltametry (CV) was conducted at a scan rate of 50 mV·s−1. Differential pulse voltammetry (DPV) was carried out with a scan rate of 10 mV·s−1, an amplitude of 25 mV, and a step potential of 10 mV. Prior to photocurrent measurements, all test solutions were degassed with high-purity nitrogen.

3. Results and Discussion

3.1. Morphological Characterization

The morphologies of the series of sensors are displayed in Figure 1. Figure 1A shows the SEM image of the bare Si substrate electrode, where the Si surface appears smooth and polished. In contrast, the silicon surface prepared by photolithography and etching exhibits a uniform and orderly columnar array structure (Figure 1B,C). The cross-sectional SEM image (Figure 1D) further reveals that these microcolumn arrays have an average diameter of approximately 20 µm, a height of approximately 100 µm, and an inter-column spacing of approximately 20 µm. Notably, this micro–nanoarray structure possesses a larger specific surface area, which can provide more reactive sites, thereby enhancing photoelectrochemical performance and accelerating nitrite sensing speed. To further confirm the effective deposition of gold, EDS analysis was performed on the Au/SiCAs, and the corresponding results are shown in Figure 1E–H and Figure S3. The results demonstrate that, in addition to Si and O elements, Au is uniformly distributed in the selected area, confirming the successful deposition of Au on the surface of the silicon column arrays by sputtering.

3.2. Optical Characterization

The optical absorption capacity is widely recognized as a crucial factor in photoelectrochemical processes. To systematically evaluate the optical absorption capabilities of the series of samples, UV-Vis diffuse reflectance spectroscopy (DRS) measurements were performed. As shown in Figure 2A, Au modification significantly enhances the optical absorption in the 200–400 nm wavelength range while diminishing absorption between 400 and 800 nm. This observation may be attributed to the strong intrinsic absorption of the 40 nm gold film in the 200–400 nm UV range, combined with its role in substantially suppressing surface reflectance, which promotes greater light penetration into the absorbing layer and leads to an apparent enhancement in absorption, while the higher reflectivity of gold in the visible spectrum reduces the material’s light absorption. The fabricated columnar array architecture on the silicon surface demonstrates superior light absorption characteristics compared to planar structures, which is attributed to the enhanced specific surface area. Furthermore, by comparing the curves of Au/Si and Au/SiCAs, it is evident that the enhancement in light absorption capacity of the ordered column structure is markedly higher in the 400 nm to 800 nm range than in the 200 nm to 400 nm range. We propose that this phenomenon arises from (1) the increased light scattering and inter-column reflections of the ordered columnar structure, (2) reduced specular reflection by the Au film, and (3) their synergistic effect in improving the overall light trapping efficiency.

3.3. Photoelectrochemical Performance

Since material performance is influenced by morphology and structure, we initially optimized the etching depth of the columnar silicon and the sputtering thickness of the gold layer at the beginning of the experiment. The test results in Figures S4–S6. It is worth nothing that as the etching depth increases, the material’s hydrophobicity rises sharply, rendering the sensor surface increasingly resistant to wetting by the test solution, which leads to a marked deterioration in performance (Figure S5E,F). Furthermore, excessively thick metallic films may compromise the substrate’s light absorption capacity, thereby impairing photoelectrochemical (PEC) performance (Figure S6E). Additionally, thicker Au layers are less economically viable. Taking these factors into account, an optimal balance a 40 nm-gold layer sputtered on 100-μm-deep columnar silicon. The subsequent analysis presents results under these optimal conditions.
Figure S7 presents the linear sweep voltammetry (LSV) results for photoanodes under simulated solar illumination. The data indicates that after depositing the Au film, the photocurrent density of the samples increases significantly. Moreover, the introduction of the column silicon structure further enhances the material’s photoelectrochemical performance (Figure S7B), which is likely attributable to the structure’s enhanced light absorption capability.
To further characterize the photoelectrochemical active surface area of the electrodes, we performed cyclic voltammetry (CV) tests (Figure 2B and Figure S8) with the same illumination. The current response of each electrode was plotted against the scan rate for comparison of the electrochemically active surface area (Figure 2C,D). The results demonstrate a linear relationship between current response and scan rate for all electrodes, indicating ideal double-layer capacitance characteristics. Comparative analysis of the slopes reveals that Au modification significantly increases the slope values (comparing Si vs. Au/Si and SiCAs vs. Au/SiCAs). This enhancement can be explained by two factors: first, Au’s high conductivity reduces charge transfer resistance, thereby improving current response sensitivity; second, the Au film optimizes the interface characteristics between silicon and the electrolyte, improving charge accumulation efficiency. Furthermore, the ordered columnar array structure showed approximately four-fold higher slope values compared to planar Si, suggesting superior ion diffusion capacity and reduced transfer resistance in the micro-nano structure. To investigate the material’s charge transfer characteristics, electrochemical impedance spectroscopy (EIS) tests were conducted in 0.1 M PBS with same illumination. The results and corresponding fitting data are presented in Figure 2E,F and Figure S9. The EIS measurements show that Au modification significantly reduces the charge transfer resistance (Rct), consistent with its excellent conductivity. Notably, the columnar array structure modification also decreases impedance, confirming that this ordered architecture facilitates charge transport and contributes to improved photoelectrochemical performance.

3.4. Photoelectrochemical Detection of Nitrite

Photoelectrochemical sensing for nitrite detection primarily relies on the electrical response generated during the redox reaction of nitrite on the electrode surface. In neutral or weakly acidic aqueous solutions, the oxidation of nitrite is typically represented as NO2− + H2O + 2h+ → NO3− + 2H+ [42,43,44]. The resulting electrical response exhibits a linear relationship with the concentration of nitrite within a certain range, enabling quantitative analysis of nitrite in the electrolyte based on this linear correlation. In our fabricated photoanodes, n-type silicon absorbs incident photons to generate electron–hole pairs. At the interface between silicon and gold, a Schottky junction is formed, whose built-in electric field facilitates the drift of photogenerated holes toward the silicon surface while suppressing the backflow of electrons into the gold layer, thereby effectively reducing carrier recombination. Driven by this electric field, the holes migrate to the surface and are efficiently collected by the surface-deposited gold (Au) layer. The Au layer serves both as a conductive medium and a protective barrier, preventing surface passivation of silicon. Furthermore, the accumulation of holes at the Au–electrolyte interface induces a positive shift in the surface potential, enabling the oxidation of adsorbed nitrite to nitrate. Overall, by leveraging the carrier separation capability of the Schottky junction, this process achieves efficient transfer and utilization of photogenerated holes from the semiconductor to the metal and ultimately to the target reactant, as illustrated in Scheme 2. To validate this mechanism, cyclic voltammetry (CV) tests were conducted in nitrite-containing electrolyte with the addition of hole scavengers (CH3OH and KI). As shown in Figure S10, the nitrite oxidation peak around 0.8 V disappears upon addition of both scavengers, confirming the proposed charge-transfer pathway.
To evaluate the performance of the prepared electrodes for photoelectrochemical nitrite sensing, we conducted photo-induced electrochemical measurements in PBS containing different NaNO2 concentrations under simulated solar illumination. Figure 3A,B show the cyclic voltammetry (CV) responses of Si, Au/Si, SiCAs, and Au/SiCAs in PBS with a NaNO2 concentration of 2.0 mmol·L−1. The results reveal that the CV curves of Si and SiCAs lack characteristic peaks, indicating that n-Si lacks specificity for detecting NO2−. In contrast, Au/Si and Au/SiCAs display distinct redox peaks at approximately 0.8 V and 0.3 V, confirming the feasibility of Au modification for nitrite detection as a catalytic layer for photoelectrochemical NO2− sensing. Figure 3C,D present the CV profiles of Au/Si and Au/SiCAs in PBSs with different concentrations of NaNO2. The linear regression equations for the Au/Si and Au/SiCAs electrodes are y = 69.246x + 6.915 and y = 330.709x + 386.576, respectively. A positive correlation between the oxidation peak current and NaNO2 concentration was observed, with both electrodes exhibiting good linearity, further supporting Au as an effective catalytic material for nitrite detection. Notably, Au/SiCAs displayed a significantly larger current response and a steeper slope in the fitting line, demonstrating the silicon columnar array enhances the photoelectrochemical sensing performance of the electrode. In summary, Au functions as an efficient catalytic layer for NO2− detection, and the integration of micro–nanoarchitectures significantly improves the sensitivity of photoelectrochemical sensing. For comparison, we conducted the same experiment under dark conditions, with the results shown in the Figure S11A,B. It can be observed that, although a linear correlation is also exhibited, the sensitivity is significantly lower than that under illuminated conditions, indicating the crucial role of photoexcitation in the detection process.
The above experimental results indicate that the prepared Au/SiCAs electrodes exhibit excellent detection performance in the high concentration range of 0–10 mmol·L−1. To further explore the electrode’s performance for nitrite detection, differential pulse voltammetry (DPV) was employed for low-concentration NaNO2 analysis with the same illumination. Owing to its superior sensitivity compared to conventional voltametric techniques, DPV is particularly suitable for trace-level analyte quantification. As shown in Figure 4, the DPV tests and fitting curves demonstrate different concentrations of nitrite using Au/SiCAs electrode in PBS. The results confirm its strong photoelectrocatalytic activity toward nitrite oxidation. Notably, within the concentration range of 1.0 × 10−5 mol·L−1 to 5.0 × 10−4 mol·L−1, the DPV current response exhibited a linear dependence on nitrite concentration (Figure 4B), with a correlation coefficient (R2) of 0.999 and a linear regression equation of y = 248.784x + 100.064. The calculated detection limit of 0.25 μmol·L−1 further confirm the sensor’s high sensitivity. Replicate measurements were performed (Figure 4B), with error bars demonstrating good reproducibility and stability. Table 1 lists the comparison of nitrite detection performance with other photoelectrochemical electrodes, revealing a lower LOD, wider linear range, and higher sensitivity, which collectively its superior performance. Furthermore, we performed the same experiment under dark conditions, as shown in Figure S11C,D. It can be seen that the current response is significantly lower and fails to exhibit a positive correlation with concentration. This demonstrates the crucial role of photoexcitation in enhancing sensitivity and lowering the detection limit.
For comparison, DPV tests were also conducted on Au/Si electrodes under identical conditions. As shown in Figure S12, the results indicate a loss of linear response at lower nitrite concentrations, further validating that the columnar array structure enhances detection sensitivity while reducing the LOD, thereby improving photoelectrochemical sensing performance.

3.5. Selectivity and Anti-Interference Performance

Selectivity is a crucial parameter in evaluating sensor performance. To systematically assess the selectivity of the Au/SiCAs electrode, amperometric tests were performed in 0.1 mol·L−1 PBS containing 2 mmol·L−1 NaNO2 alongside various potential interferents, as shown in Figure 5. The photoelectrochemical response was measured under a 0.5 V (vs. Ag/AgCl) applied bias, corresponding to the NO2− oxidation peak potential in DPV. The light source was activated at 100 s and deactivated at 200 s, with the steady-state photocurrent at 150 s used for comparative analysis. As shown in Figure 5B, the results indicate that the addition of Na+, Cl−, SO42−, K+, and NH4+ exhibited negligible interference, producing no significant current response. In contrast, strongly reducing interferents like S2− and SO32− generated detectable currents, likely due to their overlapping oxidation potentials with NO2−. Nevertheless, the NO2− response current still remained dominant, exceeding those of S2− and SO32− by factors of 2 and 3, respectively, highlighting superior specificity.
Additionally, to evaluate practical applicability, continuous detection tests were conducted with sequential interferent addition. The results (Figure S13) indicate that the electrode also maintained stable performance under dynamic conditions, further confirming its feasibility for practical applications.

3.6. Stability Test and Real Sample Analysis

In addition to specificity, long-term stability is a critical factor for sensors in practical applications. We conducted a long-term amperometric test on Au/SiCAs at an applied potential of 0.5 V to assess their stability. As shown in Figure S14A, the response of Au/SiCAs to 0.2 mol·L−1 NaNO2 decreased by only 18.7% after a 2-week period. Furthermore, the DPV measurements was monitored over a 7-week period (Figure S14B) in 50 μmol·L−1 NaNO2, revealing a mere 17.8% reduction in current response after this duration confirming its good stability.
To validate the practical applicability of the Au/SiCAs-based sensor, nitrite detection was performed in environmental water samples under simulated solar illumination. As summarized in Table 2, the measured nitrite concentrations showed excellent correlation with certified reference values, confirming the sensor’s accuracy. Recovery tests further demonstrated robust performance, with recovery rates ranging from 99.40% to 101.19%, highlighting the method’s precision and minimal matrix interference. Together, these findings establish the Au/SiCAs sensor as a reliable platform for quantitative nitrite analysis in complex aqueous systems.

4. Conclusions

This study presents a novel photoelectrochemical sensor for nitrite detection based on a sputter-deposited gold layer on photolithographically patterned silicon columnar arrays (Au/SiCAs). Compared to conventional gold-modified planar silicon electrodes (Au/Si), this sensor exhibited significantly enhanced photoelectrochemical activity, achieving a lower detection limit with dual linear ranges of 10–500 μmol·L−1 and 2–10 mmol·L−1. The physical fabrication approach (utilizing photolithography and sputtering) offers distinct advantages over chemical modification methods, including precise control of nanostructuring and improved batch-to-batch reproducibility. Electrochemical characterization revealed exceptional sensor stability and anti-interference capability during continuous operation. Furthermore, in practical testing, the sensor exhibited excellent specificity for continuous detection. Collectively, this work establishes a reliable, chemically stable platform for nitrite monitoring and proposes a generalizable framework for developing high-performance photoelectrochemical sensors via controlled physical nanostructuring. The synergistic combination of high-aspect-ratio silicon column arrays, precise photolithographic patterning, and a conformal sputtered Au film not only underpins the enhanced PEC performance for nitrite detection, but also provides a versatile and tunable architecture that can be readily adapted for the sensitive and selective detection of a broad spectrum of other analytes through surface functionalization or structural optimization.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/ma19050921/s1, Figure S1: The electrode structure of Au/SiCAs. The hatched areas indicate the regions insulated with silicone rubber. The upper section measuring 1.0 cm × 0.3 cm corresponds to the area in contact with the electrode holder. Figure S2: Front view photos of each electrode, from bottom to top: Si, Au/Si, SiCAs, and Au/SiCAs. Figure S3: EDS results for Au/SiCAs, including (A) energy spectrum and (B) mapping images. Figure S4: Cross-sectional images of SiCAs at different depths: (A) 30 μm, (B) 60 μm, (C) 80 μm, (D) 120 μm, (E) 140 μm, (F) 160 μm, (G) 200 μm. Figure S5: DPV test results of Au/SiCAs at different depths: (A) 30 μm, (B) 60 μm, (C) 80 μm, (D) 120 μm, (E) 140 μm, (F) 160 μm. Figure S6: CV test results and their fitted curves for different Au thicknesses: (A,B) 10 nm, (C,D) 20 nm, (E) 60 nm. Figure S7: LSV test results for Si, Au/Si, SiCAs, and Au/SiCAs. Figure S8: CV scan results in the non-Faradaic region for (A) Si, (B) Au/Si, and (C) SiCAs. The scan rates from inner to outer are (a) 10 mV·s−1, (b) 20 mV·s−1, (c) 40 mV·s−1, (d) 60 mV·s−1, (e) 80 mV·s−1, (f) 100 mV·s−1, and (g) 120 mV·s−1. Figure S9: EIS fitting data for each electrode. Figure S10: CV test in PBS with NaNO2 mixed with CH3OH and KI as hole scavenger. All reagent concentrations are 10 mM. Figure S11: Comparative experiment under dark conditions: (A)(B) CV test and fitted curve between 0 mM to 8 mM, (C)(D) DPV test and fitted curve, from a to h the concentration increases. Figure S12: Low-concentration DPV test for Au/Si. Figure S13: Continuity test for Au/Si. Figure S14: Stability test for Au/SiCAs: (A) comparison of current responses at one-week intervals; (B) DPV stability test over 7 weeks.

Author Contributions

Conceptualization, Z.C.; methodology, M.L.; software, M.L.; validation, Z.C., M.L. and Z.L.; formal analysis, M.L.; investigation, Z.C.; resources, X.W.; data curation, Y.L.; writing-original draft preparation, M.L.; writing-review and editing, Z.C. and J.A.; visualization, X.W.; supervision, Y.L.; project administration, Z.C.; funding acquisition, Z.C. and Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (No. 62504093), Basic Research Program of Jiangsu (No. BK20251591).

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding authors.

Acknowledgments

The authors gratefully acknowledge the financial supported by the National Natural Science Foundation of China (No. 62504093), Basic Research Program of Jiangsu (No. BK20251591).

Conflicts of Interest

The authors declare no conflict of interest.

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Materials 19 00921 sch001
Scheme 1. Preparation process of Au/SiCAs sensor for nitrite detection.
Scheme 1. Preparation process of Au/SiCAs sensor for nitrite detection.
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Materials 19 00921 g001
Figure 1. SEM images of SiCAs electrodes: (A) top view of Si electrode; (B,C) top view of SiCAs electrodes; (D) cross-section of SiCAs electrodes; EDS energy spectra of Au/SiCAs: (E) SEM image of Au/SiCAs and the corresponding EDS mapping image of (F) Si, (G) Au, and (H) O.
Figure 1. SEM images of SiCAs electrodes: (A) top view of Si electrode; (B,C) top view of SiCAs electrodes; (D) cross-section of SiCAs electrodes; EDS energy spectra of Au/SiCAs: (E) SEM image of Au/SiCAs and the corresponding EDS mapping image of (F) Si, (G) Au, and (H) O.
Materials 19 00921 g001
Materials 19 00921 g002
Figure 2. (A) DRS curves of Si, Au/Si, SiCAs, and Au/SiCAs; (B) CV scan curves of Au/SiCAs with different sweep speeds (a) 10 mV·s−1, (b) 20 mV·s−1, (c) 40 mV·s−1, (d) 60 mV·s−1, (e) 80 mV·s−1, (f) 100 mV·s−1, (g) 120 mV·s−1; (C,D) current response versus sweep speed for Si, Au/Si, SiCAs, and Au/SiCAs and their fitting results; (E,F) EIS test results and their fitting curves for Si, Au/Si, SiCAs, and Au/SiCAs.
Figure 2. (A) DRS curves of Si, Au/Si, SiCAs, and Au/SiCAs; (B) CV scan curves of Au/SiCAs with different sweep speeds (a) 10 mV·s−1, (b) 20 mV·s−1, (c) 40 mV·s−1, (d) 60 mV·s−1, (e) 80 mV·s−1, (f) 100 mV·s−1, (g) 120 mV·s−1; (C,D) current response versus sweep speed for Si, Au/Si, SiCAs, and Au/SiCAs and their fitting results; (E,F) EIS test results and their fitting curves for Si, Au/Si, SiCAs, and Au/SiCAs.
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Materials 19 00921 sch002
Scheme 2. Schematic diagram of photoelectrochemical oxidation of nitrite.
Scheme 2. Schematic diagram of photoelectrochemical oxidation of nitrite.
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Figure 3. CV tests of (A,B) Si, Au/Si, SiCAs and Au/SiCAs in PBSs with 2.0 mmol·L−1 NaNO2 solution; CV tests of (C) Au/Si and (D) Au/SiCAs in PBSs with different concentrations of NaNO2 and their fitted curves.
Figure 3. CV tests of (A,B) Si, Au/Si, SiCAs and Au/SiCAs in PBSs with 2.0 mmol·L−1 NaNO2 solution; CV tests of (C) Au/Si and (D) Au/SiCAs in PBSs with different concentrations of NaNO2 and their fitted curves.
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Figure 4. (A) DPV tests of Au/SiCAs in PBSs with different concentrations of NaNO2 and (B) fitted curves, with NaNO2 concentrations from low to high as (a) 0 μmol·L−1, (b) 10 μmol·L−1, (c) 20 μmol·L−1, (d) 50 μmol·L−1, (e) 80 μmol·L−1, (f) 100 μmol·L−1, (g) 120 μmol·L−1, (h) 150 μmol·L−1, (i) 180 μmol·L−1, (j) 200 μmol·L−1, (k) 300 μmol·L−1, (l) 400 μmol·L−1 and (m) 500 μmol·L−1.
Figure 4. (A) DPV tests of Au/SiCAs in PBSs with different concentrations of NaNO2 and (B) fitted curves, with NaNO2 concentrations from low to high as (a) 0 μmol·L−1, (b) 10 μmol·L−1, (c) 20 μmol·L−1, (d) 50 μmol·L−1, (e) 80 μmol·L−1, (f) 100 μmol·L−1, (g) 120 μmol·L−1, (h) 150 μmol·L−1, (i) 180 μmol·L−1, (j) 200 μmol·L−1, (k) 300 μmol·L−1, (l) 400 μmol·L−1 and (m) 500 μmol·L−1.
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Figure 5. Selectivity test of Au/SiCAs. (A) IT test: the light source was turned on at 100 s and turned off at 200 s; (B) Bar chart presentation of the test results, with the inset showing a partial enlargement.
Figure 5. Selectivity test of Au/SiCAs. (A) IT test: the light source was turned on at 100 s and turned off at 200 s; (B) Bar chart presentation of the test results, with the inset showing a partial enlargement.
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Table 1. Comparison of analytical performance of various photoelectrochemical electrodes for nitrite detection.
Table 1. Comparison of analytical performance of various photoelectrochemical electrodes for nitrite detection.
ElectrodeLinear Range (μM)Detection Limit (μM)Sensitivity (μA·μM−1·cm−2)Ref.
TiO2 (G a) NW b@EPNS c/Cyt C d0.5–90000.225201.79[45]
TiO2 P25/SPCS e2.2–108.7
10.9–217.4		1.3
4.3		0.02
0.006		[29]
CdS/TiO2 NRAs f/FTO1–5000.562.91[28]
BiVO4/FTO2.5–1001.50.053[46]
Zn0.5Cd0.5S/BiOCl/FTO1–100
100–600		0.41——[47]
Au/SiCAs2000–10,000
10–500		0.250.33, 0.25This work
a graphene. b nanowires. c electroconductive polymer nanosponge. d Cytochrome C. e screen-printed carbon substrates. f nanorod arrays.
Table 2. Nitrite Determination in Real Samples by the PEC Method (n = 3).
Table 2. Nitrite Determination in Real Samples by the PEC Method (n = 3).
SampleActual (μM)Detected (μM)Recovery (%)RSD (%)
110099.40 ± 2.4899.40%2.50%
2200202.39 ± 8.15101.19%4.03%
3340339.94 ± 1.7899.98%0.52%
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Li, M.; Chen, Z.; Liu, Z.; Wang, X.; Li, Y.; Ao, J. Photolithography-Enabled Au/Si Columnar Array Photoelectrochemical Sensor for High-Performance Nitrite Detection. Materials 2026, 19, 921. https://doi.org/10.3390/ma19050921

AMA Style

Li M, Chen Z, Liu Z, Wang X, Li Y, Ao J. Photolithography-Enabled Au/Si Columnar Array Photoelectrochemical Sensor for High-Performance Nitrite Detection. Materials. 2026; 19(5):921. https://doi.org/10.3390/ma19050921

Chicago/Turabian Style

Li, Miaotao, Zhiwei Chen, Zhangcheng Liu, Xiao Wang, Yang Li, and Jinping Ao. 2026. "Photolithography-Enabled Au/Si Columnar Array Photoelectrochemical Sensor for High-Performance Nitrite Detection" Materials 19, no. 5: 921. https://doi.org/10.3390/ma19050921

APA Style

Li, M., Chen, Z., Liu, Z., Wang, X., Li, Y., & Ao, J. (2026). Photolithography-Enabled Au/Si Columnar Array Photoelectrochemical Sensor for High-Performance Nitrite Detection. Materials, 19(5), 921. https://doi.org/10.3390/ma19050921

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