Quantification of caffeine in coffee cans using electrochemical measurements, machine learning, and boron-doped diamond electrodes

At a Glance

Metadata	Details
Publication Date	2024-03-26
Journal	PLoS ONE
Authors	T. Honda, Kenshin Takemura, Susumu Matsumae, Nobutomo Morita, Wataru Iwasaki
Institutions	Saga University, National Institute of Advanced Industrial Science and Technology
Citations	3
Analysis	Full AI Review Included

Quantification of Caffeine in Complex Beverages using BDD Electrodes and Machine Learning

This technical documentation analyzes the research paper “Quantification of caffeine in coffee cans using electrochemical measurements, machine learning, and boron-doped diamond electrodes” (Honda et al., 2024). It highlights the critical role of high-quality Boron-Doped Diamond (BDD) electrodes and connects the material requirements directly to 6CCVD’s advanced MPCVD diamond capabilities.

Executive Summary

The research successfully demonstrates a rapid, non-destructive method for quantifying caffeine in complex commercial beverages using Boron-Doped Diamond (BDD) electrodes combined with machine learning (ML).

Material Superiority: Heavily boron-doped polycrystalline diamond (BDD) was utilized for its wide potential window, high chemical resistance, and long-term stability, crucial for complex matrices.
Elimination of Pretreatment: The BDD electrode enabled direct electrochemical measurement of commercial coffee without solvent pretreatment, dilution, or electrolyte addition, significantly reducing analysis time and cost.
Advanced Quantification: Square Wave Voltammetry (SWV) signals were analyzed using Principal Component Analysis (PCA) and Principal Component Regression (PCR) to overcome signal interference from foreign substances.
High Accuracy: The combined electrochemical and ML approach achieved an average caffeine prediction accuracy of 93.88% (median 95.95%) compared to manufacturer-published values.
Speed Advantage: Measurement time was reduced to 2 minutes, drastically faster than traditional High-Performance Liquid Chromatography (HPLC), which requires 120 minutes and extensive pretreatment.
Scalability Potential: This methodology is highly applicable for rapid, high-throughput quality control and sensing applications in food, pharmaceutical, and environmental monitoring.

Technical Specifications

The following hard data points were extracted from the research, detailing the BDD electrode properties and performance metrics.

Parameter	Value	Unit	Context
Electrode Material	Heavily Boron-Doped PCD	N/A	Working Electrode
Boron Concentration	5E20	cm^-3	Doping level (p+)
Film Thickness	2	µm	BDD layer on Si substrate
Substrate Roughness (Ra)	< 0.1	nm	Before film growth
Electrochemical Stability Range	-2.4 to 2.5	V	Cyclic Voltammetry (CV) sweep range
Caffeine Oxidation Peak	1.6	V	Primary redox reaction potential
Double Layer Capacitance (Cdl)	0.18	µF/cm²	Measured in 1 g/L NaCl solution
Average Prediction Accuracy	93.88	%	Graded evaluation result (BDD + ML)
Median Prediction Accuracy	95.95	%	Graded evaluation result (BDD + ML)
Measurement Time	2	minutes	Direct SWV measurement

Key Methodologies

The BDD electrode fabrication and subsequent electrochemical analysis relied on precise control over material synthesis and signal processing.

BDD Synthesis (Hot-Filament Chemical Vapor Deposition)

Substrate Preparation: Si (100) substrates were chemically cleaned and preseeded with diamond nanopowders to facilitate nucleation.
Gas Composition: Hydrogen (H₂), Methane (CH₄), and Trimethylboron gases were introduced.
Gas Ratios: The Methane/Hydrogen gas ratio was maintained at 3% during growth.
Pressure and Temperature: Total pressure was maintained at 1.3 kPa. Tungsten filament wires were resistively heated to a temperature of 2200°C.
Doping and Termination: The resulting BDD film had a boron concentration of 5E20 cm^-3 and was hydrogen terminated.

Electrochemical Measurement (Square Wave Voltammetry)

System: Standard three-electrode system was used (BDD Working Electrode, Ag/AgCl Reference Electrode, Pt coil Counter Electrode).
Technique: Square Wave Voltammetry (SWV) was performed to measure caffeine levels.
Conditions: Measurements were taken directly from commercial coffee (3 ml sample) without pretreatment or added electrolyte.
Electrode Cleaning: A 2 V voltage was applied for 100 s between measurements to clean the BDD surface.

Quantification Algorithm (Machine Learning)

Data Acquisition: SWV spectral data (voltage-current values) were collected for known and unknown solutions.
Feature Extraction: Two types of features were extracted:
- Concrete Information (X): Coordinates with the highest contribution ratio and variance (details).
- Abstract Information (Y): Area around the 1.6 V caffeine oxidation peak (whole information).
Dimensionality Reduction: Principal Component Analysis (PCA) was applied to the multivariate spectral data.
Regression: Principal Component Regression (PCR) was used to predict unknown caffeine content based on the combined (X+Y) feature sets.
Final Prediction: The median of the stepwise evaluation values (Ave1, Ave2, Ave3) was output as the final quantitative value.

6CCVD Solutions & Capabilities

The success of this research hinges on the quality and specific doping of the BDD electrode, a core competency of 6CCVD. Our ability to deliver highly customized MPCVD diamond materials ensures researchers can replicate, scale, and advance this high-accuracy sensing technology.

Applicable Materials for Replication and Extension

To replicate the high performance and chemical stability achieved in this study, researchers require heavily boron-doped polycrystalline diamond (PCD) with ultra-low surface roughness.

6CCVD Material Solution	Specification Match	Customization Potential
Heavy Boron-Doped PCD	Boron concentration up to 1E21 cm^-3 (matching or exceeding the 5E20 cm^-3 used).	Essential for high conductivity and wide potential window required for complex electrochemical sensing.
Polished PCD Wafers	Polishing capability to achieve Ra < 5 nm (for inch-size PCD).	Ensures the smooth, stable electrode interface necessary for low background current and reliable Cdl measurements.
Custom Thickness PCD	Thicknesses ranging from 0.1 µm up to 500 µm.	Allows optimization of the BDD film thickness (2 µm used in the study) for specific device integration or mechanical stability requirements.
Silicon Substrates	Standard Si (100) substrates with BDD film growth.	6CCVD provides BDD films grown on Si, matching the substrate used in the research for seamless integration into existing semiconductor fabrication processes.

Customization Potential for Advanced Sensing Arrays

Scaling this technology from a single-chip electrode to a high-throughput sensor array requires advanced fabrication capabilities. 6CCVD is uniquely positioned to support this transition:

Large Area Electrodes: We offer PCD plates and wafers up to 125 mm in diameter, enabling the fabrication of large-scale sensor arrays for simultaneous, multi-sample analysis.
Custom Metalization: Integration of BDD electrodes into electrochemical cells often requires robust electrical contacts. 6CCVD provides in-house metalization services, including Ti/Pt/Au, Ti/W, and Cu layers, ensuring low-resistance ohmic contacts for reliable signal transmission.
Precision Processing: Our advanced laser cutting and etching services allow for the creation of custom electrode geometries and precise patterning necessary for microfluidic or multi-sensor chip designs.

Engineering Support

The combination of electrochemistry and machine learning requires deep expertise in both material science and application engineering.

Application Expertise: 6CCVD’s in-house PhD team specializes in the electrochemical properties of diamond. We can assist researchers in optimizing BDD material selection (doping level, surface termination, roughness) for similar complex matrix analysis projects (e.g., environmental toxins, medical diagnostics, or other food quality control applications).
Stability and Reproducibility: We provide consultation on achieving the long-term response stability and high chemical resistance demonstrated in this paper, ensuring reliable performance even under repeated high-voltage cycling.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Electrochemical measurements, which exhibit high accuracy and sensitivity under low contamination, controlled electrolyte concentration, and pH conditions, have been used in determining various compounds. The electrochemical quantification capability decreases with an increase in the complexity of the measurement object. Therefore, solvent pretreatment and electrolyte addition are crucial in performing electrochemical measurements of specific compounds directly from beverages owing to the poor measurement quality caused by unspecified noise signals from foreign substances and unstable electrolyte concentrations. To prevent such signal disturbances from affecting quantitative analysis, spectral data of voltage-current values from electrochemical measurements must be used for principal component analysis (PCA). Moreover, this method enables highly accurate quantification even though numerical data alone are challenging to analyze. This study utilized boron-doped diamond (BDD) single-chip electrochemical detection to quantify caffeine content in commercial beverages without dilution. By applying PCA, we integrated electrochemical signals with known caffeine contents and subsequently utilized principal component regression to predict the caffeine content in unknown beverages. Consequently, we addressed existing research problems, such as the high quantification cost and the long measurement time required to obtain results after quantification. The average prediction accuracy was 93.8% compared to the actual content values. Electrochemical measurements are helpful in medical care and indirectly support our lives.

Tech Support

Original Source

DOI: https://doi.org/10.1371/journal.pone.0298331

References

2005 - Determination of caffeine and its metabolites in urine by capillary electrophoresis‐mass spectrometry [Crossref]
2014 - Beverage caffeine intakes in the US [Crossref]
2002 - Effects of caffeine on bone and the calcium economy [Crossref]
1986 - Caffeine consumption during pregnancy and association with late spontaneous abortion. [Crossref]
2012 - Voltammetric determination of caffeine in beverage samples on bare boron-doped diamond electrode [Crossref]
2018 - HPLC method for quantification of caffeine and its three major metabolites in human plasma using fetal bovine serum matrix to evaluate prenatal drug exposure
1999 - Quantitative HPLC analysis of sunscreens and caffeine during in vitro percutaneous penetration studies [Crossref]
2008 - Measurement of caffeine in coffee beans with UV/vis spectrometer [Crossref]
2013 - Optimization of a UV-vis spectrometric method for caffeine analysis in tea, coffee and other beverages
2000 - Quantification of caffeine by off-line TLC-MS