Blood ammonia testing is a fundamental and important clinical indicator in liver function assessment, diagnosis of hepatic encephalopathy, and screening for metabolic diseases. However, the concentration of blood ammonia is extremely low in the blood, and the sample is easily contaminated by exogenous ammonia. The requirements for reagent stability and reaction sensitivity in the detection process are also much higher than those for conventional biochemical tests. How to accurately capture trace changes in blood ammonia in complex clinical samples is the key and difficult point in the development of in vitro diagnostic reagents.
Color reaction: the core process of blood ammonia detection
The widely used blood ammonia measurement methods in clinical practice are mostly based on the principle of enzyme coupling reaction. The ammonia in the sample reacts with glutamic acid under the catalysis of glutamine synthetase, generating glutamine and consuming ATP; Subsequently, the reaction signal is converted into hydrogen peroxide (H ₂ O ₂) through an auxiliary enzyme system; Finally, under the catalysis of peroxidase (POD), H ₂ O ₂ undergoes oxidative condensation with the chromogenic substrate, generating colored quinone imine compounds whose absorbance is proportional to blood ammonia concentration.
The key to this reaction pathway lies in the colorimetric system, which directly determines the strength and stability of the detection signal. If the color reaction is unstable, even if the early enzymatic reaction is accurate, there may still be deviations in the final result.
The technical bottleneck of traditional color rendering system
The commonly used chromogenic substrates for early blood ammonia detection include 4-aminoantipyrine (4-AAP) and MBTH (3-methyl-2-benzothiazolinone hydrazone). 4-AAP has a lower cost, but its molar absorptivity is not high, which affects the detection sensitivity; At the same time, its water solubility is limited, which restricts the reaction efficiency. Although MBTH has high sensitivity, its chemical stability is poor, especially in the air where it is easily oxidized, leading to the gradual failure of reagents during storage or the operation of fully automatic biochemical analyzers, and the reproducibility of detection results is difficult to guarantee.
In the context of pursuing high-throughput and automated testing in clinical laboratories, the onboard stability of colorimetric systems has become an unavoidable technical challenge in reagent development.
Introduction of TOOS: From Structural Optimization to Performance Enhancement
The application of the novel chromogenic substrate TOOS reagent(N-ethyl-N - (2-hydroxy-3-sulfopropyl) -3-methylaniline) provides a feasible solution to the above problems. The TOOS molecular structure contains sulfopropyl and hydroxyl groups, endowing it with excellent water solubility and steric hindrance effect, which can effectively inhibit the occurrence of non-specific oxidation reactions.
In practical applications, TOOS often forms a dual color system with MBTH. Under the catalysis of peroxidase, the two can efficiently couple to form stable quinone imine chromophores, with a maximum absorption wavelength between 550-570 nm and a molar absorptivity of 3.92 × 10 ⁴ L · mol ⁻¹ · cm ⁻¹. The signal intensity is significantly improved. More importantly, with appropriate formulation support, this combined color development system can maintain long-term chemical stability and meet the continuous detection requirements of fully automatic biochemical analyzers.
Multiple guarantees of stability
In addition to the molecular structure advantage of TOOS itself, the overall stability improvement of the reagent also benefits from the optimization of formula design. In the TOOS+MBTH colorimetric system, an appropriate amount of oxygen scavenger (such as ascorbic acid derivatives) and non-ionic surfactant can be added to protect MBTH molecules and reduce their oxidation risk during storage and use.
At the same time, TOOS has stable chemical properties within the physiological pH range and will not cause side reactions with buffer solutions (such as Tris), inorganic salts, or enzyme components, which helps to ensure inter batch consistency of reagents and reduce fluctuations in clinical testing results. This characteristic is particularly important for diagnostic reagents that require long-term storage and cross batch use.
Hubei Xindesheng Material Technology Co., Ltd. has long been dedicated to the research and production of high-performance chromogenic substrates such as TOOS, and is committed to providing stable raw material supply and professional technical support for the in vitro diagnostic industry. If you have any recent purchasing needs, please click on the official website to learn more details or contact me directly!
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