Noninvasive glucose detection in exhaled breath condensate

Abstract

Two-thirds of patients with diabetes avoid regularly monitoring their blood glucose levels because of the painful and invasive nature of current blood glucose detection. As an alternative to blood sample collection, exhaled breath condensate (EBC) has emerged as a promising noninvasive sample from which to monitor glucose levels. However, this dilute sample matrix requires sensors capable of detecting glucose with high resolution at nanomolar and micromolar concentrations. Recent developments in EBC collection methods and highly sensitive glucose biosensors provide a path toward enabling robust and sensitive glucose detection in EBC. This review addresses current and emerging EBC collection and glucose sensing modalities capable of quantifying glucose in EBC samples. We highlight the opportunities and challenges for development and integration of EBC glucose detection systems that will enable clinically robust and accurate EBC glucose measurements for improved glycemic control.

Figure 1.. Respiratory droplet aerosolization and dilution.

When droplets are released from the surface of the airway lining, they undergo evaporation. However, as they travel up the respiratory tract, they are also diluted by water vapor. Hence, the droplets are much larger when they are collected as exhaled breath condensate. Reprinted from Effros et al. with permission from [Permissions pending from American Journal of Respiratory and Critical Care Medicine (permissions@thoracic.org)].

Figure 2.. Typical collection method and relevant components for condensation of exhaled breath.

Reproduced from Mutlu et al. with permission from [Permissions pending from American Journal of Respiratory and Critical Care Medicine (permissions@thoracic.org)].

Figure 3.. Components of exhaled air from various regions of respiratory tract.

Adapted from Effros et al. The box indicates the respiratory zone of the airway tract in which solutes of interest are present in the alveolar fluid lining and respiratory droplets in the bronchi. This region is represented by phase III of the capnography plot above, which is characterized by the CO₂ plateau. Anatomical dead space air is present in the upper region of the respiratory tract (outside of the box). It does not participate in gas exchange and is represented by phase I and II of the capnography plot. Airway diagram reprinted with permission from [Permissions pending from American Journal of Physiology – Lung Cellular and Molecular Physiology https://www.physiology.org/author-info.permissions].

Figure 4.. Temperature-based selective condensing mechanism for EBC developed by Tankasala et al..

a) Temperature and CO₂ profile comparison from breathing profile of a human subject; b) Temperature-based valve actuation. The valve action (black) is displayed for periods where the valve is open. The threshold (green) is continuously updated based on the average temperature range of the last three breaths; c) Device set-up for exhaled breath condensate collection and analysis. Temperature, valve actuation, and time for collection are recorded. The sample is then analyzed for glucose content. Sample can also be analyzed for total protein concentration and pH; d) Glucose concentrations from EBC samples collected with different temperature selection threshold. Reprinted with permission from Tankasala et al. [Permissions pending from 2018 40th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) https://ieeexplore.ieee.org/document/8513393].

Figure 5.. Schematic representation of the progression of electrochemical glucose biosensors.

a) First generation sensor that uses molecular oxygen as a cofactor; b) second generation sensor that uses artificial redox mediators; c) third generation sensor that relies on direct electron transfer between the enzyme and electrode. Reprinted from Wang with permission from [Permissions pending from Chemical Reviews https://pubs.acs.org/doi/10.1021/cr068123a].

Figure 6.. Schematic of the ZnO nanorod array deposited on the gate area of the AlGaN/GaN HEMT sensor.

a) The HEMTs were fabricated through several steps of molecule beam epitaxy, chemical vapor deposition, inductively coupled plasma etching, and e-beam deposition GOx is immobilized on the nanorods. b) Glucose was detected through the changes in the electrostatic interactions between GOx and the nanorods, which were measured by the drain current of the HEMT. Reproduced from Kang et al. with permission from [Permissions pending from Journal of Diabetes Science & Technology]

Figure 7.. Assembly of CDTe Quantum Dots complexed with glucose oxidase and schematic of glucose sensing.

Reprinted from Cao et al. with permission from [Permissions pending from Chemistry – A European Journal].

Figure 8.. Representative image of the glucose binding protein and its conformational change upon binding to glucose.

Reprinted from Siegrist et al. with permission from [Permissions pending from Sensors and Actuators B: Chemical].

Figure 9.. Schematic of Ni-NTA immobilized GBP for fiber optic glucose detection.

a) Incorporation of immobilized GBP on optical fiber. The beads are entrapped within a nylon tube on the tip of an optical fiber and secured in place with nylon mesh; b) Set-up of fiber optic GBP sensor with min-fluorometer for signal acquisition and image processing. Image reproduced from Tiangco et al. with permission from [Permissions pending from Sensors and Actuators B: Chemical].

Figure 10.. Application for QD-FRET in GBP glucose biosensor.

GBP can be covalently conjugated to a QD. Initially, a galactosamine quencher (gal-BHQ2) will be bound at the binding pocket of GBP and result in FRET quenching of the QD luminescence. When samples containing glucose are introduced, the gal-BHQ2 is displaced by glucose and photoluminescence of the QD will increase.

Figure 11.. Chemical structure of the CdTe quantum dots complexed with Concanavalin Abound gold nanoparticles for FRET-based detection of glucose.

Image reprinted from Tang et al. with kind permission from [Permissions pending from Chemistry – A European Journal].