Real-Time Analysis of Oxygen Gradient in Oocyte Respiration Using a High-Density Microelectrode Array

Abstract

Physiological events related to oxygen concentration gradients provide valuable information to determine the state of metabolizing biological cells. The existing oxygen sensing methods (i.e., optical photoluminescence, magnetic resonance, and scanning electrochemical) are well-established and optimized for existing in vitro analyses. However, such methods also present various limitations in resolution, real-time sensing performance, complexity, and costs. An electrochemical imaging system with an integrated microelectrode array (MEA) would offer attractive means of measuring oxygen consumption rate (OCR) based on the cell’s two-dimensional (2D) oxygen concentration gradient. This paper presents an application of an electrochemical sensor platform with a custom-designed complementary-metal-oxide-semiconductor (CMOS)-based microchip and its Pt-coated surface MEA. The high-density MEA provides 16,064 individual electrochemical pixels that cover a 3.6 mm × 3.6 mm area. Utilizing the three-electrode configuration, the system is capable of imaging low oxygen concentration (18.3 µM, 0.58 mg/L, or 13.8 mmHg) at 27.5 µm spatial resolution and up to 4 Hz temporal resolution. In vitro oxygen imaging experiments were performed to analyze bovine cumulus-oocytes-complexes cells OCR and oxygen flux density. The integration of a microfluidic system allows proper bio-sample handling and delivery to the MEA surface for imaging. Finally, the imaging results are processed and presented as two-dimensional (2D) heatmaps, representing the dissolved oxygen concentration in the immediate proximity of the MEA. This paper provides the results of real-time 2D imaging of OCR of live cells/tissues to gain spatial and temporal dynamics of target cell metabolism.

Microfluidic chip as a promising evaluation method in assisted reproduction: A systematic review

“…Two of the four microspectrometry studies classified the oocytes into top‐ and low‐quality (Figure 4f). 82,83 Less frequently reported properties included current impedance ( n = 2) 85,86 and oxygen concentration ( n = 1) 87 …”

“…Twenty studies characterized oocytes using microfluidics (Table 1). 56,[69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87] Microfluidic chips can measure large numbers of oocytes with high throughput and sensitivity. 88 Seven studies deformed oocytes to test their mechanical properties (Figure 4a-d), [69][70][71][72][73][74][75] including one that applied injection force to test oocyte mechanics (Figure 4c), 70 and three that used compression force.…”

“…82,83 Less frequently reported properties included current impedance (n = 2) 85,86 and oxygen concentration (n = 1). 87…”

Advanced strategies for single embryo selection in assisted human reproduction: A review of clinical practice and research methods

“…These methods should possess features such as high sensitivity, non-invasiveness, a low detection limit, compatibility with other types of measurements (such as temperature, pH, chemical, and impedance), and reproducibility [136]. Previous methods, such as fluorescence and spectrophotometry, were not suitable for clinical use due to their low sensitivity and invasiveness [137].…”

“…Kurosawa et al [137] developed a novel device that employs a chip-sensing embryo respiration monitoring system, which automates the measurement of oxygen consumption using electrochemical methods. Tedjo et al [136] utilized an electrochemical imaging system equipped with an integrated microelectrode array to measure the oxygen consumption of bovine oocytes. This system was found to enable imaging at low oxygen concentrations in vitro.…”