Enhanced sensitivity and detection range of FRET-based vitamin B12 nanosensor

Emerging Roles of Vitamin B12 in Aging and Inflammation

Vitamin B12 (cobalamin) is an essential nutrient for humans and animals. Metabolically active forms of B12-methylcobalamin and 5-deoxyadenosylcobalamin are cofactors for the enzymes methionine synthase and mitochondrial methylmalonyl-CoA mutase. Malfunction of these enzymes due to a scarcity of vitamin B12 leads to disturbance of one-carbon metabolism and impaired mitochondrial function. A significant fraction of the population (up to 20%) is deficient in vitamin B12, with a higher rate of deficiency among elderly people. B12 deficiency is associated with numerous hallmarks of aging at the cellular and organismal levels. Cellular senescence is characterized by high levels of DNA damage by metabolic abnormalities, increased mitochondrial dysfunction, and disturbance of epigenetic regulation. B12 deficiency could be responsible for or play a crucial part in these disorders. In this review, we focus on a comprehensive analysis of molecular mechanisms through which vitamin B12 influences aging. We review new data about how deficiency in vitamin B12 may accelerate cellular aging. Despite indications that vitamin B12 has an important role in health and healthy aging, knowledge of the influence of vitamin B12 on aging is still limited and requires further research.

An Adenosylcobalamin Specific Whole-Cell Biosensor

Vitamin B12 (cobalamin) is essential for human health and its deficiency results in anemia and neurological damage. Vitamin B12 exists in different forms with various bioactivity but most sensors are unable to discriminate between them. Here, a whole-cell agglutination assay that is specific for adenosylcobalamin (AboB12), which is one of two bioactive forms, is reported. This biosensor consists of Escherichia coli that express the AdoB12 specific binding domain of CarH at their surface. In the presence of AdoB12, CarH forms tetramers, which leads to specific bacterial cell-cell adhesions and agglutination. These CarH tetramers disassemble upon green light illumination such that reversion of the bacterial aggregation can serve as internal quality control. The agglutination assay has a detection limit of 500 nм AdoB12, works in protein-poor biofluids such as urine, and has high specificity to AdoB12 over other forms of vitamin B12 as also demonstrated with commercially available supplements. This work is a proof of concept for a cheap and easy-to-readout AdoB12 sensor that can be implemented at the point-of-care to monitor high-dose vitamin B12 supplementation.

Real time optical detection of gold in living cells through genetically-encoded probe

To study the efflux of gold (Au) in living cells, a genetically encoded fluorescence resonance energy transfer (FRET)-based sensor has been developed. The gold-sensing domain GolB from Salmonella typhimurium has been fused to the N- and C-termini of the FRET pair enhanced cyan fluorescent protein (ECFP) and Venus respectively. In living cells, this probe is highly selective and sensitive to gold and it can withstand changes in variable pH ranges. GolSeN-25, the most efficient sensor variant, binds gold with an affinity (K_d) of 0.3 × 10⁻⁶ M, covering gold concentrations of nM to μM, and can be used for non-invasive real-time in vivo gold measurement in living cells. A simple and sensitive FRET probe was designed for the detection of gold with high selectivity and can be applied to the analysis of real samples.

To study the efflux of gold (Au) in living cells, a genetically encoded fluorescence resonance energy transfer (FRET)-based sensor has been developed.

The quantum dot-FRET-based detection of vitamin B12 at a picomolar level

Herein we report the picomolar level detection of vitamin B12 (VB12) using orange-red emitting ligand-free Mn²⁺-doped ZnS quantum dots (QDs; λ _em = 587 nm) in an aqueous dispersion. Sensing was achieved following the quenching of the luminescence of the Mn²⁺-doped ZnS QDs with an increasing concentration of VB12. The Stern-Volmer constant was determined to be 5.2 × 10¹⁰ M^-1. Importantly, the Mn²⁺-doped ZnS QDs exhibited high sensitivity towards VB12, with a limit of detection as low as 1.15 ± 0.06 pM (in the linear range of 4.9-29.4 pM) and high selectivity in the presence of interfering amino acids, metal ions, and proteins. Notably, a Förster resonance energy transfer (FRET) mechanism was primarily proposed for the observed quenching of luminescence of Mn²⁺-doped ZnS QDs upon the addition of VB12. The Förster distance (R _o) and energy transfer efficiency (E) were calculated to be 2.33 nm and 79.3%, respectively. Moreover, the presented QD-FRET-based detection may bring about new avenues for future biosensing applications.