Fused deposition modeling (FDM) based 3D printing of microelectrodes and multi-electrode probes

3D-printed electrodes for electrochemical detection of environmental analytes

Environmental monitoring faces increasing demands for rapid, sensitive, and cost-effective analytical methods to detect various pollutants. Three-dimensional (3D) printing technology has emerged as a transformative approach for fabricating electrochemical sensors, offering unprecedented flexibility in electrode design and potential for customization. This comprehensive review examines recent advances in 3D-printed electrochemical sensors for environmental analysis, focusing on manufacturing technologies, materials development, and surface modification strategies. We analyze various printing approaches, including fused deposition modeling, stereolithography, and selective laser melting, discussing their relative advantages and limitations for electrode fabrication. The review explores conductive materials development, from carbon-based composites to novel metal-containing filaments, and examines crucial surface modification techniques that enhance sensor performance. Key applications in environmental monitoring are evaluated, including the detection of heavy metals, pathogens, antibiotics, and organophosphates, with particular attention to analytical performance metrics and real-world applicability. Technical challenges are critically assessed, including limitations in printing resolution, material conductivity, and long-term stability. The review concludes by identifying promising research directions, such as the integration of advanced materials and the development of automated manufacturing processes, highlighting opportunities for improving sensor performance and commercial viability in environmental monitoring applications.

Printing technologies for the fabrication of ion-selective electrodes

The fabrication of ion-selective electrodes (ISEs) via printing technologies such as screen-printing, inkjet printing, and 3D printing is attracting increasing attention due to the superb reproducibility and scalability of these technologies. In contrast to traditional manual casting, coating, and assembling procedures often used in research labs, printing methods are much more compatible with manufacturing processes in industry and, therefore, are easier to scale up. In this paper, we first summarized and compared the printing mechanisms and ink requirements of screen printing, inkjet printing, and 3D printing technologies. Then we present an overview of how different printing technologies can create sensor components, such as electrical contact layers, ion-to-electron transduction layers, ion sensing membranes, reference electrode membranes, insulation layers, and microfluidic/detection housings. The printing protocol, ink material, and sensor performance are highlighted for a few selected ISEs. This review concludes with a summary of the advantages and drawbacks of various printing technologies.

Novel disposable and portable 3D-printed electrochemical apparatus for fast and selective screening of 25E-NBOH in forensic samples

The advent of new psychoactive substances (NPS) has caused enormous difficulty for legal control since they are rapidly commercialized, and their chemical structures are routinely altered. In this aspect, derivatives phenethylamines, such as 25E-NBOH, have received great attention in the forensic scenario. Hence, we propose portable and cost-effective (U$ 5.00) 3D-printed devices for the electrochemical screening of 25E-NBOH for the first time. The cell and all electrodes were printed using acrylonitrile butadiene styrene filament (insulating material) and conductive filament (graphite embedded in a polylactic acid matrix), respectively, both by the fused deposition modeling (FDM) 3D printing technique. The electrochemical apparatus enables micro-volume analysis (50-2000 μL), especially important for low sample volumes. A mechanistic route for the electrochemical oxidation of 25E-NBOH is proposed based on cyclic voltammetric data, which showed two oxidation processes around +0.75 V and +1.00 V and a redox pair between +0.2 and -0.2 V (vs. graphite ink pseudo-reference). A fast and sensitive square-wave voltammetry method was developed, which exhibited a linear working range from 0.85 to 5.1 μmoL-1, detection limit of 0.2 μmol L-1, and good intra-electrode precision (n = 10, RSD <5.3 %). Inter-electrode measurements (n = 3, RSD <9.8 %) also attested that the electrode production process is reproducible. Interference tests in the presence of other drugs frequently found in blotting paper indicated high selectivity of the electrochemical method for screening of 25E-NBOH. Screening analysis of blotting paper confirmed the presence of 25E-NBOH in the seized samples. Moreover, a recovery percentage close to 100 % was found for a spiked saliva sample, suggesting the method's usefulness for quantitative purposes aimed at information on recent drug use.

3D printed graphite-based electrode coupled with batch injection analysis: An affordable high-throughput strategy for atorvastatin determination

This work integrated a lab-made conductive graphite/polylactic acid (Grp/PLA, 40:60% w/w) filament into a 3D pen to print customized electrodes (cylindrical design). Thermogravimetric analysis validated the incorporation of graphite into the PLA matrix, while Raman spectroscopy and scanning electron microscopy images indicated a graphitic structure with the presence of defects and highly porous, respectively. The electrochemical features of the 3D-printed Gpt/PLA electrode were systematically compared to that achieved using commercial carbon black/polylactic acid (CB/PLA, from Protopasta®) filament. The 3D printed Gpt/PLA electrode "in the native form" provided lower charge transfer resistance (Rct = 880 Ω) and a more kinetically favored reaction (K⁰ = 1.48 × 10^-3 cm s^-1) compared to the 3D printed CB/PLA electrode (chemically/electrochemically treated). Moreover, a method by batch injection analysis with amperometric detection (BIA-AD) was developed to determine atorvastatin (ATR) in pharmaceutical and water samples. Using the 3D printed Gpt/PLA electrode, a wider linear range (1-200 μmol L^-1), sensitivity (3-times higher), and lower detection limit (LOD = 0.13 μmol L^-1) were achieved when compared to the CB/PLA electrode. Repeatability studies (n = 15, RSD <7.3%) attested to the precision of the electrochemical measurements, and recovery percentages between 83 and 108% confirmed the accuracy of the method. Remarkably, this is the first time that ATR has been determined by the BIA-AD system and a low-cost 3D-printed device. This approach is promising to be implemented in research laboratories for quality control of pharmaceuticals and can also be useful for on-site environmental analysis.

Three-Dimensional-Printed Molds from Water-Soluble Sulfate Ceramics for Biocomposite Formation through Low-Pressure Injection Molding

Powder mixtures of MgSO₄ with 5-20 mol.% Na₂SO₄ or K₂SO₄ were used as precursors for making water-soluble ceramic molds to create thermoplastic polymer/calcium phosphate composites by low pressure injection molding. To increase the strength of the ceramic molds, 5 wt.% of tetragonal ZrO₂ (Y₂O₃-stabilized) was added to the precursor powders. A uniform distribution of ZrO₂ particles was obtained. The average grain size for Na-containing ceramics ranged from 3.5 ± 0.8 µm for MgSO₄/Na₂SO₄ = 91/9% to 4.8 ± 1.1 µm for MgSO₄/Na₂SO₄ = 83/17%. For K-containing ceramics, the values were 3.5 ± 0.8 µm for all of the samples. The addition of ZrO₂ made a significant contribution to the strength of ceramics: for the MgSO₄/Na₂SO₄ = 83/17% sample, the compressive strength increased by 49% (up to 6.7 ± 1.3 MPa), and for the stronger MgSO₄/K₂SO₄ = 83/17% by 39% (up to 8.4 ± 0.6 MPa). The average dissolution time of the ceramic molds in water did not exceed 25 min.

Carbon Black Integrated Polylactic Acid Electrodes Obtained by Fused Deposition Modeling: A Powerful Tool for Sensing of Sulfanilamide Residues in Honey Samples

Sulfanilamide (SFL) is used to prevent infections in honeybees. However, many regulatory agencies prohibit or establish maximum levels of SFL residues in honey samples. Hence, we developed a low-cost and portable electrochemical method for SFL detection using a disposable device produced through 3D printing technology. In the proposed approach, the working electrode was printed using a conductive filament based on carbon black and polylactic acid and it was associated with square wave voltammetry (SWV). Under optimized SWV parameters, linear concentration ranges (1-10 μmol L^-1 and 12.5-35.0 μmol L^-1), a detection limit of 0.26 μmol L^-1 (0.05 mg L^-1), and suitable RSD values (2.4% for inter-electrode; n = 3) were achieved. The developed method was selective in relation to other antibiotics applied in honey samples, requiring only dilution in the electrolyte. The recovery values (85-120%) obtained by SWV were statistically similar (95% confidence level) to those obtained by HPLC, attesting to the accuracy of the analysis and the absence of matrix interference.

Covalently modified enzymatic 3D-printed bioelectrode

Three-dimensional (3D) printing has showed great potential for the construction of electrochemical sensor devices. However, reported 3D-printed biosensors are usually constructed by physical adsorption and needed immobilizing reagents on the surface of functional materials. To construct the 3D-printed biosensors, the simple modification of the 3D-printed device by non-expert is mandatory to take advantage of the remote, distributed 3D printing manufacturing. Here, a 3D-printed electrode was prepared by fused deposition modeling (FDM) 3D printing technique and activated by chemical and electrochemical methods. A glucose oxidase-based 3D-printed nanocarbon electrode was prepared by covalent linkage method to an enzyme on the surface of the 3D-printed electrode to enable biosensing. X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the glucose oxidase-based biosensor. Direct electrochemistry glucose oxidase-based biosensor with higher stability was then chosen to detect the two biomarkers, hydrogen peroxide and glucose by chronoamperometry. The prepared glucose oxidase-based biosensor was further used for the detection of glucose in samples of apple cider. The covalently linked glucose oxidase 3D-printed nanocarbon electrode as a biosensor showed excellent stability. This work can open new doors for the covalent modification of 3D-printed electrodes in other electrochemistry fields such as biosensors, energy, and biocatalysis.