Zhennan Wang

A fully integrated standalone portable cavity ringdown breath acetone analyzer

Breath analysis is a promising new technique for nonintrusive disease diagnosis and metabolic status monitoring. One challenging issue in using a breath biomarker for potential particular disease screening is to find a quantitative relationship between the concentration of the breath biomarker and clinical diagnostic parameters of the specific disease. In order to address this issue, we need a new instrument that is capable of conducting real-time, online breath analysis with high data throughput, so that a large scale of clinical test (more subjects) can be achieved in a short period of time. In this work, we report a fully integrated, standalone, portable analyzer based on the cavity ringdown spectroscopy technique for near-real time, online breath acetone measurements. The performance of the portable analyzer in measurements of breath acetone was interrogated and validated by using the certificated gas chromatography-mass spectrometry. The results show that this new analyzer is useful for reliable online (online introduction of a breath sample without pre-treatment) breath acetone analysis with high sensitivity (57 ppb) and high data throughput (one data per second). Subsequently, the validated breath analyzer was employed for acetone measurements in 119 human subjects under various situations. The instrument design, packaging, specifications, and future improvements were also described. From an optical ringdown cavity operated by the lab-set electronics reported previously to this fully integrated standalone new instrument, we have enabled a new scientific tool suited for large scales of breath acetone analysis and created an instrument platform that can even be adopted for study of other breath biomarkers by using different lasers and ringdown mirrors covering corresponding spectral fingerprints.

Optimal wavelength selection for visible diffuse reflectance spectroscopy discriminating human and nonhuman blood species

The species identification of human and nonhuman blood is an important and immediate challenge for forensic science, veterinary purposes, and wildlife preservation. Current methods used to identify the species of origin of a blood stain are limited in scope and destructive to the sample. We have previously demonstrated that visible diffuse reflectance spectroscopy combined with the PLS-DA method can realize the discrimination of human and nonhuman blood. Research studies have proved that the application of appropriate wavelength variable selection prior to model calibration can be greatly beneficial in providing a more reliable and parsimonious model. Apart from improving the prediction ability, the usage of variable selection will also reduce the experimental work. Moreover, the cost of a high-performance optical emission spectrometer and a supercontinuum white light laser source is comparatively high. In contrast, diode lasers, fixed-filter spectrometers and diode array spectrometers, which are very common products, greatly cut the cost of measurement systems. The key to use this kind of spectrometer is to find the optimal wavelength combination for getting a fine calibration. In this paper, we used the Equidistant Combination Multiple Linear Regression (ECMLR) method for wavelength selection. Compared with the results of full-spectrum PLS-DA, the ECMLR method could enhance the performance of identified models. Happily, for time related validation, the prediction effect of the ECMLR method was slightly better than that of the full-spectrum PLS-DA method. The overall results sufficiently demonstrate that the PLS-DA model constructed using wavelength variables selected by an appropriate wavelength variable method can be more effective and accurate.

Breath Acetone Analysis of Diabetic Dogs Using a Cavity Ringdown Breath Analyzer

Some dogs develop a form of diabetes mellitus (DM) similar to that seen in children (juvenile, or Type 1 DM). It is characterized by concurrent high blood glucose (BG) and urine glucose concentrations. Elevated breath acetone concentrations have been observed in Type 1 DM in humans, though a quantitative correlation between breath acetone and BG has yet to be determined. The study of breath acetone in diabetic dogs might allow the use of breath acetone as a biomarker for diabetes in both humans and animals. We report on breath acetone analysis of 51 dogs (37 nondiabetic dogs and 14 diabetic dogs). Breath samples were collected and simultaneous BG levels (if applicable) were measured. Breath acetone tests were conducted using a real-time breath acetone analyzer that is based on the cavity ringdown spectroscopy technique. Absolute breath acetone concentrations (upper limits) were determined without the need for breath sample preconcentration and measurement calibration. For the 37 nondiabetic dogs, their exhaled breath acetone concentrations ranged from 0.16 to 2.42 parts per million (ppm). For the 14 diabetic dogs, breath acetone concentrations ranged from 0.17 to 5.80 ppm with a BG range of 30-750 mg/dL. The mean breath acetone concentration in the 14 diabetic dogs is 1.25 ppm, which is higher than that in the 37 nondiabetic dogs, i.e., 0.60 ppm. The mean breath acetone concentration in nondiabetic dogs, 0.60 ppm, is close to the mean breath acetone concentration in healthy humans. Although diabetic dogs exhibit elevated mean breath acetone concentration, as in human Type 1 DM, no correlation was found between breath acetone concentration and BG level in the diabetic dogs in this paper.

A Portable Real-Time Ringdown Breath Acetone Analyzer: Toward Potential Diabetic Screening and Management

Breath analysis has been considered a suitable tool to evaluate diseases of the respiratory system and those that involve metabolic changes, such as diabetes. Breath acetone has long been known as a biomarker for diabetes. However, the results from published data by far have been inconclusive regarding whether breath acetone is a reliable index of diabetic screening. Large variations exist among the results of different studies because there has been no “best-practice method” for breath-acetone measurements as a result of technical problems of sampling and analysis. In this mini-review, we update the current status of our development of a laser-based breath acetone analyzer toward real-time, one-line diabetic screening and a point-of-care instrument for diabetic management. An integrated standalone breath acetone analyzer based on the cavity ringdown spectroscopy technique has been developed. The instrument was validated by using the certificated gas chromatography-mass spectrometry. The linear fittings suggest that the obtained acetone concentrations via both methods are consistent. Breath samples from each individual subject under various conditions in total, 1257 breath samples were taken from 22 Type 1 diabetic (T1D) patients, 312 Type 2 diabetic (T2D) patients, which is one of the largest numbers of T2D subjects ever used in a single study, and 52 non-diabetic healthy subjects. Simultaneous blood glucose (BG) levels were also tested using a standard diabetic management BG meter. The mean breath acetone concentrations were determined to be 4.9 ± 16 ppm (22 T1D), and 1.5 ± 1.3 ppm (312 T2D), which are about 4.5 and 1.4 times of the one in the 42 non-diabetic healthy subjects, 1.1 ± 0.5 ppm, respectively. A preliminary quantitative correlation (R = 0.56, p < 0.05) between the mean individual breath acetone concentration and the mean individual BG levels does exist in 20 T1D subjects with no ketoacidosis. No direct correlation is observed in T1D subjects, T2D subjects, and healthy subjects. The results from a relatively large number of subjects tested indicate that an elevated mean breath acetone concentration exists in diabetic patients in general. Although many physiological parameters affect breath acetone, under a specifically controlled condition fast (<1 min) and portable breath acetone measurement can be used for screening abnormal metabolic status including diabetes, for point-of-care monitoring status of ketone bodies which have the signature smell of breath acetone, and for breath acetone related clinical studies requiring a large number of tests.

Study of breath acetone and its correlations with blood glucose and blood beta-hydroxybutyrate using an animal model with lab-developed type 1 diabetic rats

Breath acetone has long been a known biomarker for diabetes. However whether breath acetone analysis can be used for clinical applications ultimately depends on how breath acetone concentration is quantitatively and accurately related to an established clinical diagnostic parameter(s). Numerous studies of breath acetone using human subjects have been done, yet this fundamental question remains unaddressed because complex physiological processes and various conditions of humans are relevant to change of breath acetone. We report for the first time on the study of breath acetone and its correlations with blood glucose (BG) and blood β-hydroxybutyrate (BHB) using an animal model of rats. 18 non-diabetic healthy rats and 20 lab-developed type 1 diabetic (T1D) rats were used as two subject groups. Breath gas samples from the rats were collected using a noninvasive oral intubation method that was compared with the intrusive and time-consuming method of tracheostomy. Breath acetone concentrations were measured using a cavity ringdown spectroscopy based breath analyzer without using additional sample preparation, sample pre-concentration, or calibration. The measured breath acetone concentrations were in the ranges of 1.9–4.3 ppm (part per million by volume) for the 20 T1D rats and 1.4–2.8 ppm for the 18 non-diabetic healthy rats. Simultaneous BG and blood BHB levels were also obtained. Results show that breath acetone, BG, and blood BHB in the T1D rat group all have significant difference from the one in the healthy rat group (P < 0.05). A significant positive relationship (Pearson’s r = 0.644, P < 0.05) between breath acetone and blood BHB was found to exist in both subject groups. A significant negative relationship (Pearson’s r = −0.678, P < 0.05) between breath acetone and BG was found in the T1D rats only. However, the relationship between breath acetone and BG shifts from negative to weakly positive when T1D rats were treated with insulin. Furthermore, results from a multiple linear regression model analysis reveal that breath acetone has a predictive nature for blood BHB in T1D rats, which confirms the sole report in T1D human subjects. This result suggests that the animal model can be used for large scale clinical study to help address fundamentals in human breath analysis in some cases.

Detection of Melanoma Cancer Biomarker Dimethyl Disulfide Using Cavity Ringdown Spectroscopy at 266 nm

Skin cells emit volatile organic compounds (VOCs), and some of them can be used as biomarkers for screening specific diseases. Dimethyl disulfide (DMDS) has been recently reported as a biomarker of melanoma skin cancer (Kwak et al. “Volatile Biomarkers from Human Melanoma Cells”. J. Chromatogr. B. 2013. 931: 90–96.). With the motivation of diagnosing melanoma using DMDS as its biomarker, we explore the potential of measuring DMDS using an advanced laser spectroscopic technique as an alternative method. We report on the first DMDS measurements using an experimental system based on cavity ringdown spectroscopy (CRDS). The test samples were mixtures of DMDS vapor and nitrogen in different concentrations. Two sampling methods were investigated to dilute the DMDS sample to low concentrations for ringdown measurements. The results showed that the ringdown system responded to various DMDS concentrations linearly and a theoretical detection limit of sub-ppb (parts per billion) could be achieved at the absorption wavelength of 266 nm. This ringdown system exhibited a high dynamic range for DMDS measurements, from ppm (parts per million) to ppt (parts per trillion) levels, given different laser wavelengths used. The feasibility of developing a portable melanoma screening sensor using the CRDS technique was also demonstrated in this study.

Application of LaserBreath-001 for breath acetone measurement in subjects with diabetes mellitus

Breath acetone is a promising biomarker of diabetes mellitus. With an integrated standalone, on-site cavity ringdown breath acetone analyzer, LaserBreath-001, we tested breath samples from 23 type 1 diabetic (T1D) patients, 312 type 2 diabetic (T2D) patients, 52 healthy subjects. In the cross-sectional studies, the obtained breath acetone concentrations were higher in the diabetic subjects compared with those in the control group. No correlation between breath acetone and simultaneous BG was observed in the T1D, T2D, and healthy subjects. A moderate positive correlation between the mean individual breath acetone concentrations and the mean individual BG levels was observed in the 20 T1D patients without ketoacidosis. In a longitudinal study, the breath acetone concentrations in a T1D patient with ketoacidosis decreased significantly and remained stable during the 5-day hospitalization. The results from a relatively large number of subjects tested indicate that an elevated mean breath acetone concentration exists in diabetic patients in general. Although many physiological parameters affect breath acetone concentrations, fast (<1 min) and on site breath acetone measurement can be used for diabetic screening and management under a specifically controlled condition.