A diamond particle measuring just 70 nanometers—thousands of times smaller than a human hair—has successfully entered living yeast cells in a laboratory at the University of Groningen in the Netherlands. There, it functions as a quantum sensor, detecting the presence of free radicals, harmful molecules long believed to contribute to aging and various degenerative diseases. The research formed part of the doctoral dissertation of drg. Aryan Morita, M.Sc., Ph.D., a faculty member in the Department of Dental Biomedicine at the Faculty of Dentistry, Universitas Gadjah Mada, who completed and defended his PhD at the University of Groningen on November 3, 2020, under the supervision of Prof. Romana Schirhagl. The research represents an important milestone: for the first time, diamond magnetometry was used to measure free radicals directly, in real time, and at subcellular resolution in living cells.
Free Radicals: Small Enemies That Are Difficult to Capture
Free radicals are molecules with unpaired electrons that are naturally produced as byproducts of cellular metabolism, particularly in the mitochondria. At balanced levels, these molecules play important roles in various physiological processes. Problems arise when their production becomes excessive or when the body’s antioxidant defense systems fail to function adequately—a condition known as oxidative stress.
Oxidative stress is closely associated with cellular aging, DNA damage, cardiovascular disease, and cancer. The free radical theory of aging even proposes that damage caused by free radicals is a major driver of aging at the cellular level.
Unfortunately, measuring free radicals is far from easy. They occur at very low concentrations—ranging from nanomolar to micromolar levels—and have extremely short lifespans. Existing methods, such as fluorescent dyes like H₂DCFDA or gene-expression analysis using quantitative PCR, each have significant limitations: they lack specificity, capture the “history” of a sample rather than its current state, are susceptible to photobleaching, and cannot precisely reveal where within the cell the radicals are located.
Diamond as a Quantum Sensor
The solution proposed by drg. Aryan Morita and his team involves exploiting atomic defects in the diamond crystal known as nitrogen-vacancy (NV) centers. These defects have a unique ability to convert magnetic signals from their surrounding environment into optical signals that can be detected using a confocal microscope.
The principle is straightforward: when free radicals are present near an NV center, they generate magnetic “noise,” or spin noise, that accelerates the decay of the NV center’s quantum state. This is measured as the T1 relaxation time. The shorter the T1, the higher the concentration of free radicals surrounding the diamond particle. This technique is known as diamond magnetometry, or more specifically, relaxometry.
Its advantages are clear. Unlike fluorescent dyes, which are consumed as they react with free radicals, diamond is optically stable and does not undergo photobleaching. It is also non-toxic to cells and can be used for long-term measurements in the same cell, at the same location, repeatedly.
“With this T1 signal, we were able to distinguish the responses of mutant strains and young and old cells, with or without H₂O₂ and antioxidants. This technique opens new possibilities for faster and more efficient studies of free radicals at the single-cell level.” — drg. Aryan Morita, M.Sc., Ph.D., in his dissertation, Diamond Nanosensors for Age and Stress Related Changes in Cells (2020)
From Cellular Entry to Measurements in Living Cells
The research did not begin directly with free-radical measurements. Instead, drg. Aryan Morita developed a systematic four-stage approach over four years.
Stage one: developing a method to introduce diamond particles into cells. The yeast Saccharomyces cerevisiae was selected as a model organism because of its relevance to aging research. However, its thick cell wall prevents particles from entering naturally. The solution was spheroplasting, in which the cell wall is enzymatically removed and lipid-coated diamond particles (FND-lip) are introduced into the cells through membrane fusion. This approach significantly increased particle uptake without compromising cell viability.
Stage two: monitoring the fate of diamond particles as cells divide. Yeast cells undergo asymmetric division, producing a larger mother cell and a smaller daughter cell. Surprisingly, most of the particles were transferred to daughter cells or expelled from the cells rather than being retained in mother cells, as occurs with harmful protein aggregates. This suggests that the diamond particles were not recognized as harmful by the cellular mechanisms.
Stage three: directing the diamond particles toward the cell nucleus using antibodies specific to the nuclear pore complex (NPC). The results showed that 70% of antibody-conjugated diamond particles successfully reached the surface of the nucleus, compared with only 20% of particles without antibodies.
Stage four—and the most critical: measuring actual free radicals in living cells. Four yeast strains were tested: a wild-type strain and three mutant strains (sod1Δ, tor1Δ, and pex19Δ) with different metabolic characteristics. The cells were observed when young, after oxidative stress induced by 1% H₂O₂, after aging for 24 hours, and after treatment with the antioxidant L-ascorbic acid.
The results were consistent with the free radical theory of aging: older cells exhibited a higher free-radical burden. More interestingly, two long-lived mutant strains, tor1Δ and pex19Δ, had lower free-radical burdens, providing a potential mechanistic explanation for their extended lifespan. Antioxidant treatment also measurably reduced free-radical levels, particularly in young cells.
Implications for Dentistry and Biomedical Science
Although the research used yeast cells as a model, its relevance to dentistry and biomedicine extends much further. Oxidative stress and free-radical accumulation are involved in the pathogenesis of various oral conditions, ranging from periodontal disease and dental caries to oral cancer. The ability to measure free radicals precisely and in real time at the single-cell level opens new opportunities for understanding oxidative damage in periodontal tissues, dental pulp, and oral mucosa.
Moreover, the ability of these diamond sensors to directly evaluate antioxidant effects at the single-cell level could provide a powerful screening tool for potential therapeutic compounds, including substances being investigated to prevent aging in oral tissues.
The research was funded by an LPDP scholarship from the Ministry of Finance of the Republic of Indonesia and has resulted in several publications in internationally recognized journals, including Particle and Particle Systems Characterization and Nanomaterials, as well as a manuscript submitted to Nature Nanotechnology.
A diamond particle one-thousandth the diameter of a human red blood cell now carries enormous potential: the ability to observe what has long remained hidden within the smallest units of life.
Authors: Achmad Zam Zam Aghasy, DDS, M.Kes.; Hazra Alifia Muharam
Photo: Freepik
Sumber DOI: https://doi.org/10.33612/diss.136220127