Recent Advances in Sensing Materials Targeting Clinical Volatile Organic Compound (VOC) Biomarkers: A Review

Abstract

In general, volatile organic compounds (VOCs) have a high vapor pressure at room temperature (RT). It has been reported that all humans generate unique VOC profiles in their exhaled breath which can be utilized as biomarkers to diagnose disease conditions. The VOCs available in exhaled human breath are the products of metabolic activity in the body and, therefore, any changes in its control level can be utilized to diagnose specific diseases. More than 1000 VOCs have been identified in exhaled human breath along with the respiratory droplets which provide rich information on overall health conditions. This provides great potential as a biomarker for a disease that can be sampled non-invasively from exhaled breath with breath biopsy. However, it is still a great challenge to develop a quick responsive, highly selective, and sensitive VOC-sensing system. The VOC sensors are usually coated with various sensing materials to achieve target-specific detection and real-time monitoring of the VOC molecules in the exhaled breath. These VOC-sensing materials have been the subject of huge interest and extensive research has been done in developing various sensing tools based on electrochemical, chemoresistive, and optical methods. The target-sensitive material with excellent sensing performance and capturing of the VOC molecules can be achieved by optimizing the materials, methods, and its thickness. This review paper extensively provides a detailed literature survey on various non-biological VOC-sensing materials including metal oxides, polymers, composites, and other novel materials. Furthermore, this review provides the associated limitations of each material and a summary table comparing the performance of various sensing materials to give a better insight to the readers.

A critical insight into porous organic polymers (POPs) and its perspectives for next-generation chemiresistive exhaled breath sensing: a state-of-the-art review

“…31 Oxidative stress and metabolic changes are the two main pathways through which VOCs occur in the exhaled breath, either after exchange through the lungs or through direct degassing of the disease-specific VOCs by the malignant cells in the respiratory tract lining or gastrointestinal tract. 32…”

“…The urea or ornithine cycle converts the excess ammonia into urea, which is then excreted through the kidney as urine. 32 The cycle occurs inside the liver and kidney; thus, any dysfunction associated with the kidney and liver will increase the concentration of ammonia in the exhaled breath, which can be observed through exhaled breath analysis. In the case of NO x , the nitrate-nitrite-nitric acid pathway is the only pathway to remove the excess nitrogen oxide contents from the body, and any disruption in this pathway leads to an increase in the nitrogen oxide content, which can be monitored through exhaled breath analysis.…”

“…Increased nitrogen oxide concentration in the human body leads to serious pulmonary diseases. 32 The list of a few potential exhaled breath biomarkers and their corresponding disease profiles has been presented in Table 1.…”

“…31 Oxidative stress and metabolic changes are the two main pathways through which VOCs occur in the exhaled breath, either aer exchange through the lungs or through direct degassing of the disease-specic VOCs by the malignant cells in the respiratory tract lining or gastrointestinal tract. 32 Ammonia plays a signicant role in nutritional aspects such as the synthesis of essential as well as nonessential amino acids, maintaining acid-base levels of body uids, and synthesis of nitrogenous bases (purines and pyrimidines) of nucleotides, which are important in the formation of DNA and RNA, the nucleic acids important for carrying mostly all the cellular processes.…”

Metabolic insights at the finish line: deciphering physiological changes in ultramarathon runners through breath VOC analysis

“…Due to the non-invasive nature of collection and the convenience for repeated sampling within a short period, breath has emerged in recent years as a potential biological matrix for the diagnosis and monitoring of various diseases [5]. The volatile organic compounds (VOCs) contained in human exhaled breath can be derived from a variety of metabolic processes in the body.…”