Simultaneous Determination of Uric Acid and Caffeine by Flow Injection Using Multiple-Pulse Amperometry

At a Glance

Metadata	Details
Publication Date	2023-06-29
Journal	Biosensors
Authors	Ademar Wong, Anderson M. Santos, Maria H. A. Feitosa, Orlando Fatibello‐Filho, Fernando C. Moraes
Institutions	Universidade Federal de São Carlos
Citations	5
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Advanced Biosensing

Executive Summary

This document analyzes the application of cathodically pretreated Boron-Doped Diamond (CPT-BDD) electrodes in a Flow Injection Analysis (FIA) system utilizing Multiple-Pulse Amperometry (MPA) for the simultaneous determination of Uric Acid (UA) and Caffeine (CAF).

Core Achievement: Successful development of a highly sensitive, stable, and low-cost electrochemical method for simultaneous UA and CAF detection in complex matrices (river water, synthetic urine).
Material Superiority: The use of a CPT-BDD electrode (8000 ppm B) resulted in a predominantly hydrogen-terminated surface, significantly enhancing the oxidation peak current and overall electrochemical activity compared to anodic pretreatment.
Ultra-Low Detection Limits: The method achieved exceptional limits of detection (LOD) in the low nanomolar range: 1.1 x 10^-8 mol L^-1 for UA and 1.3 x 10^-8 mol L^-1 for CAF.
High Performance Metrics: Demonstrated wide linear concentration ranges (up to 22 µM for UA), excellent repeatability (Relative Standard Deviation < 4.1%), and high recovery rates (98-104%).
Operational Efficiency: The FIA-MPA system allows for high throughput, capable of performing 126 analytical determinations per hour, making it highly advantageous for clinical and environmental monitoring.
6CCVD Value: This research validates 6CCVD’s high-quality BDD material as the ideal platform for next-generation, high-sensitivity electrochemical biosensors requiring wide potential windows and minimal adsorption effects.

Technical Specifications

The following hard data points were extracted from the research paper detailing the optimized performance and experimental conditions of the CPT-BDD sensor.

Parameter	Value	Unit	Context
BDD Doping Concentration	8000	ppm	Working Electrode Film
Working Electrode Exposed Area	0.66	cm²	Used for current density calculation
Supporting Electrolyte	0.10	mol L^-1	H₂SO₄ Solution
UA Oxidation Potential (E₁)	0.80	V	vs. Ag/AgCl
CAF Oxidation Potential (E₂)	1.4	V	vs. Ag/AgCl
Cathodic Pretreatment (CPT) Current Density	-0.04	A cm^-2	Applied for 180 s (Optimal)
Optimal Flow Rate (FIA)	3.8	mL min^-1	Carrier Solution
Optimal Injection Volume	250	µL	Sample Volume
Optimal Pulse Time (MPA)	150	ms	Potential Pulse Duration
UA Limit of Detection (LOD)	1.1 x 10^-8	mol L^-1	Equivalent to 11 nM
CAF Limit of Detection (LOD)	1.3 x 10^-8	mol L^-1	Equivalent to 13 nM
UA Linear Range	5.0 x 10^-8 to 2.2 x 10^-5	mol L^-1	Wide dynamic range
Recovery Rates (UA/CAF)	98 to 104	%	Tested in River Water and Synthetic Urine

Key Methodologies

The experiment relied on precise control over the BDD surface chemistry and optimized FIA-MPA parameters to achieve high sensitivity and selectivity.

Electrode Material Selection: A Boron-Doped Diamond (BDD) film (8000 ppm) on a silicon wafer was used as the working electrode, chosen for its wide potential window and low adsorption properties.
Surface Cleaning: The BDD electrode was cleaned using ultrapure water and ethanol in an ultrasonic bath for 3 minutes to remove surface impurities.
Cathodic Pretreatment (CPT): The optimal surface termination was achieved by applying a cathodic current density of -0.04 A cm^-2 for 180 seconds in 0.50 mol L^-1 H₂SO₄ solution, resulting in a predominantly hydrogen-terminated surface.
Electrolyte Optimization: Cyclic voltammetry confirmed that 0.10 mol L^-1 H₂SO₄ provided the best electrochemical response for both UA and CAF oxidation.
Potential Selection: Hydrodynamic voltammograms were used to select the two optimal potential pulses for MPA: 0.80 V (for UA oxidation only) and 1.4 V (for simultaneous UA and CAF oxidation).
FIA Parameter Tuning: The flow rate (3.8 mL min^-1), injection volume (250 µL), and pulse time (150 ms) were optimized to maximize peak current and minimize adsorption effects.
Simultaneous Quantification: A correction factor (CF = 1.2 ± 0.1) was calculated and applied to the current measured at 1.4 V to accurately subtract the UA contribution, allowing for the precise determination of CAF concentration.

6CCVD Solutions & Capabilities

The successful implementation of the CPT-BDD electrode for high-sensitivity FIA-MPA biosensing directly aligns with 6CCVD’s core material and customization capabilities. We are uniquely positioned to supply the materials and engineering support required to replicate, scale, and advance this research.

Applicable Materials

Research Requirement	6CCVD Material Recommendation	Technical Specification & Value
High-Purity BDD Film (8000 ppm B)	Heavy Boron-Doped Polycrystalline Diamond (BDD PCD)	We supply MPCVD BDD wafers with customizable doping levels (e.g., 5000 ppm to 10,000 ppm) to ensure optimal conductivity and electrochemical performance for high-sensitivity detection.
High Stability/Low Adsorption	Optical Grade Single Crystal Diamond (SCD)	For ultra-high precision applications or fundamental studies, our SCD material (Ra < 1 nm) offers unparalleled surface quality, minimizing background noise and maximizing the effective potential window.
Large-Scale Sensor Production	Large-Area PCD Wafers	6CCVD offers PCD plates/wafers up to 125mm in diameter, enabling cost-effective scaling from R&D to commercial manufacturing of flow-cell sensors.

Customization Potential

The research utilized a specific electrode geometry (0.66 cm² exposed area) and required precise electrical contacts. 6CCVD offers comprehensive customization services to meet these exact engineering needs:

Custom Dimensions and Shaping: We provide precision laser cutting and machining services to produce BDD plates and wafers in any required geometry, ensuring seamless integration into custom FIA flow cells or microfluidic systems.
Thickness Control: We can supply BDD films with thicknesses ranging from 0.1 µm up to 500 µm, allowing researchers to optimize material usage and device architecture.
Integrated Metalization: The use of reference and auxiliary electrodes requires reliable electrical contacts. 6CCVD offers in-house metalization capabilities, including deposition of Ti/Pt/Au, W, Pd, or Cu contacts, directly onto the diamond substrate for robust, low-resistance connections.
Polishing Services: Our advanced polishing achieves surface roughness (Ra) < 5 nm on inch-size PCD, critical for minimizing non-specific adsorption and ensuring stable baseline currents in amperometric measurements.

Engineering Support

6CCVD’s in-house PhD team specializes in diamond surface chemistry and electrochemical applications. We offer direct consultation to assist researchers and engineers in replicating or extending this work:

Surface Termination Optimization: We provide expert guidance on selecting and implementing optimal surface treatments (e.g., CPT for hydrogen termination) to maximize the efficiency of FIA-MPA biosensing projects involving purines, xanthines, or other complex organic molecules.
Electrode Design for Flow Systems: Consultation on optimizing electrode geometry and integration into microfluidic or flow injection systems to maximize mass transport and signal-to-noise ratios.

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

View Original Abstract

The present study reports the development and application of a flow injection analysis (FIA) system for the simultaneous determination of uric acid (UA) and caffeine (CAF) using cathodically pretreated boron-doped diamond electrode (CPT-BDD) and multiple-pulse amperometry (MPA). The electrochemical profiles of UA and CAF were analyzed via cyclic voltammetry in the potential range of 0.20-1.7 V using 0.10 mol L−1 H2SO4 solution as supporting electrolyte. Under optimized conditions, two oxidation peaks at potentials of 0.80 V (UA) and 1.4 V (CAF) were observed; the application of these potentials using multiple-pulse amperometry yielded concentration linear ranges of 5.0 × 10−8-2.2 × 10−5 mol L−1 (UA) and 5.0 × 10−8-1.9 × 10−5 mol L−1 (CAF) and limits of detection of 1.1 × 10−8 and 1.3 × 10−8 mol L−1 for UA and CAF, respectively. The proposed method exhibited good repeatability and stability, and no interference was detected in the electrochemical signals of UA and CAF in the presence of glucose, NaCl, KH2PO4, CaCl2, urea, Pb, Ni, and Cd. The application of the FIA-MPA method for the analysis of environmental samples resulted in recovery rates ranging between 98 and 104%. The results obtained showed that the BDD sensor exhibited a good analytical performance when applied for CAF and UA determination, especially when compared to other sensors reported in the literature.

Tech Support

Original Source

DOI: https://doi.org/10.3390/bios13070690

References

2017 - Gout: An old disease in new perspective—A review [Crossref]
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2017 - Development of new analytical methods for the determination of caffeine content in aqueous solution of green coffee beans [Crossref]
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2013 - Determination of Caffeine: A Comprehensive Review on Electrochemical Methods [Crossref]
2017 - HPLC determination of caffeine in coffee beverage [Crossref]
2020 - Colorimetric determination of uric acid based on the suppression of oxidative etching of silver nanoparticles by chloroauric acid [Crossref]
2007 - Determination of serum uric acid using high-performance liquid chromatography (HPLC)/isotope dilution mass spectrometry (ID-MS) as a candidate reference method [Crossref]