By putting on these gloves and touching them, you can tell with your naked eyes whether the nitrite content exceeds the standard?

Produced by: Science Popularization China

Author: Yang Liang, Li Lingfei (Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences)

Producer: China Science Expo

Editor's note: In order to unveil the mystery of scientific work, the China Science Popularization Frontier Science Project launched a series of articles called "Me and My Research", inviting scientists to write articles themselves, share their scientific research experiences, and create a scientific world. Let us follow the explorers at the forefront of science and technology and embark on a journey full of passion, challenges, and surprises.

I believe everyone knows something about nitrite. As a nitrogen-containing inorganic compound that is ubiquitous in nature, it is an important part of the nitrogen cycle. It can be used as an additive in food to extend the shelf life, but excessive intake can cause poisoning and even turn into a carcinogen. At the same time, nitrite also plays a subtle role in organisms, such as regulating vascular function and enhancing immune and antibacterial capabilities. Its research is not only related to food safety, but also touches on the deep mechanisms of life sciences.

In order to more accurately detect the presence of nitrite , our research team (Jiang Changlong and Yang Liang's research team from the Energy Materials and Device Manufacturing Research Department of the Institute of Solid State Physics, Hefei Institutes of the Chinese Academy of Sciences) recently successfully designed a new method and prepared a technology for rapid detection of nitrite by fluorescence visualization , making new progress in real-time synchronous visualization detection of nitrite. The related research was published in the journal Hazardous Materials.

Why research new methods of detecting hazardous substances?

In fact, in recent years, inspectors have been able to identify hazards in the environment by using traditional techniques such as electrochemistry, colorimetry, UV-visible absorption, chemiluminescence, capillary electrophoresis, spectrophotometry and chromatography. However, these methods often have cumbersome detection procedures, expensive instruments, poor visual semi-quantitative capabilities or time-consuming problems, which together hinder their practical application.

The fluorescent visualization detection technology we developed has the advantages of simplicity, rapidity, high sensitivity and easy visualization, and is a strong candidate for the analysis of environmental hazards.

For example, the new materials and methods we have developed, combined with sensor devices (such as gloves), can help us determine whether the nitrite content in food exceeds the standard by just touching it with the naked eye.

AG. Schematic diagram of ratiometric fluorescent material combined with glove sensor for nitrite detection

(Image source: author’s article)

AC. Demonstration of ratiometric fluorescent material combined with glove sensor to detect nitrite on mobile phone sensing platform (quantitative detection of nitrite content)

(Image source: author’s article)

What is fluorescence visualization rapid detection technology? Why use fluorescence?

Fluorescence is a physical phenomenon. When a substance at room temperature absorbs the energy of incident light of a certain wavelength (usually ultraviolet rays or X-rays), it enters an excited state and emits a longer wavelength of light (usually in the visible light band) with lower energy than the absorbed light in a shorter time. This type of emitted light is called fluorescence . Fluorescence usually has a longer emission wavelength, different colors, and can continue to emit light for a period of time after the excitation stops, but the intensity will gradually weaken until it disappears.

The mechanism of fluorescence detection is based on the process that a specific molecule transitions to an excited state (increased chemical reaction activity) after absorbing light energy, and then releases energy in the form of light radiation to return to the ground state (the lowest energy and most stable), i.e., fluorescence emission. This process not only depends on the molecular structure, but is also affected by environmental factors.

Glow sticks

(Photo source: veer photo gallery)

We can use a balloon to simulate the mechanism of fluorescence detection. We first inflate the balloon, which corresponds to the transition of a specific molecule to an excited state after absorbing light energy; then we pop the balloon, which is the process of releasing energy and returning to the ground state. The generation of fluorescence is similar to this process.

How to use this characteristic of fluorescence for detection?

We have innovatively proposed a detection method - rapid fluorescence visualization detection technology. We first use ultraviolet light to excite the fluorophore, and then observe the generation, quenching or intensity changes of fluorescence with the naked eye to achieve rapid and visual detection of the object to be tested. This technology has significant advantages such as low cost, simple operation, easy to carry and high sensitivity.

In the field of food analysis, fluorescence visualization rapid detection technology has been widely used to detect harmful substances in food, such as heavy metal ions, pesticide residues and additives, etc. This technology changes the fluorescence signal of the luminescent substance through the interaction between the fluorescence sensor and the object to be tested, thereby achieving rapid qualitative and quantitative detection of the target object.

Spraying pesticides

(Photo source: veer photo gallery)

From monochromatic fluorescence to ratiometric fluorescence, fluorescent materials have gradually improved

In order to better apply the fluorescence phenomenon, scientists need to maximize the advantages of fluorescent materials. To this end, it is important to develop a variety of fluorescent materials suitable for different environments. As two key fluorescence detection methods, ratio fluorescence and monochromatic fluorescence differ in multiple dimensions, and these differences have a profound impact on improving analytical sensitivity, selectivity, and reliability.

Monochromatic fluorescence focuses on the measurement of fluorescence intensity at a single wavelength. This method is simple and easy to use, and is one of the most basic and widely used methods in fluorescence analysis. However, monochromatic fluorescence detection is susceptible to external interference, such as light source stability, detector sensitivity, and sample matrix effects, which may have a significant impact on its results.

Ratio fluorescence technology , as an advanced fluorescence detection strategy, is based on simultaneously monitoring the changes in fluorescence signals at two or more wavelengths and calculating the ratio between these signals. The advantage of this method is its inherent self-calibration property, which can partially offset the errors caused by external factors such as fluctuations in excitation light intensity, uneven sample concentration, or changes in optical system efficiency.

Ratiometric fluorescence significantly improves the stability and accuracy of measurements by comparing the relative changes in fluorescence intensity at different wavelengths rather than the absolute intensity. In addition, when the fluorescent probe is properly designed to respond to different analytes or environmental changes, ratiometric fluorescence can also provide rich molecular information and enhance the selectivity and sensitivity of detection.

However, ratiometric fluorescence, which has so many advantages, also has high requirements on materials. The research of ratiometric fluorescent materials requires comprehensive consideration of the structural design, preparation process and application requirements of the materials, which is a complex and challenging scientific research task.

Our research developed a new type of dual-emission ratiometric fluorescent material.

Mechanism of Detecting Nitrite Using Dual-Emission Ratio Fluorescent Materials

(Image source: author’s article)

This material produces visible optical color changes after exposure to nitrite and has excellent resistance to photobleaching. These properties make it have great application potential in real life. For example, this material can be combined with sensor devices (such as gloves) to verify whether nitrite exceeds the standard through its unique dual emission ratio fluorescence characteristics.

The performance of the new material in nitrite detection not only provides an innovative solution for the detection of dangerous substances in food and the environment, but also develops a new research direction. In the future, we will continue to conduct in-depth research and expand applications, and look forward to this new material playing a more important role.