Sodium Ion Detection & Analysis

Sodium (Na) is an essential element and electrolyte in biology, and is important to both cellular and electrical function. Sodium ions (Na+) are involved in a number of biochemical processes, including the maintenance of normal cellular homeostasis, blood pressure, and extracellular fluid volume via osmotic action. Sodium ions also regulate pH and electrolyte balances, and play crucial roles in the mechanisms of potassium ion (K+) and ATPase activity. Additionally, sodium ions help to generate the action potentials in nervous, cardiac, and various muscle tissues, and help transport nutrients and substrates through plasma membranes.

Sodium ion concentration in the body and blood is controlled primarily by the endocrine and renal systems. In particular, the secretion of aldosterone and anti-natriuretic peptide control total body sodium concentration. Additionally, the antidiuretic hormone (ADH) is secreted in response to an increased osmolality or decreased blood pressure, which in turn regulates sodium concentration. As sodium is so widely connected to cellular function, so too is it connected with physiology.

Association to Disease

---

The normal range for physiological sodium levels is between 135–145 mM, and an abnormal concentration of sodium could be related to adrenal gland issues, diabetes, heart failure, kidney disease, cirrhosis, or even ketonuria. Generally, pathologic increases or decreases in total body sodium are associated with corresponding increases or decreases in extracellular and plasma volume. In addition, hyponatremia (low sodium levels) can occur in patients with nephrotic syndrome, excessive vomiting and diarrhea while hypernatremia (high sodium levels) may develop in patients suffering from liver disease, or excessive burns. Many times, quantitative detection of sodium is urgently required to provide simplified diagnosis and quick treatment. Nevertheless, a simple technology that can accurately quantify sodium in the real time with excessive potassium present is an ongoing challenge.

Historically, sodium concentrations in clinical settings have been determined by ion chromatography, gravimetry, potentiometric titration, flame photometry, and atomic emission spectroscopy. These methods, while useful, require expensive, complex protocols that must be performed by trained personnel. They are lengthy, prone to error, and are sometimes only semi-quantitative. Today, quantitative assay kits and reagents are commercially available for easy, simple quantitation of sodium. More recently, novel constructs used in research have continued to emerge that can also effectively quantitate sodium in complex samples.

 

Detection Methods

---

Fluorescent Indicators

Multiple, multi-faceted, fluorescent indicators for detecting sodium exist that possess the ability to estimate sodium gradients in isolated mitochondria, measure intracellular sodium ion levels, or determine sodium efflux in cells. They can also be used to correlate changes in intracellular sodium with calcium (Ca2+) and magnesium (Mg2+) ion concentrations, intracellular pH, and membrane potential, done in combination with other fluorescent indicators. A large challenge of an effective fluorescent sodium sensor is not only in its ability to attract sodium ions at the physiologically relevant range, but also in its ability to discriminate between potassium ions and other physiological cations. This can be difficult as cytoplasmic sodium ion concentrations are normally very low compared to potassium, and vice versa for extracellular ion concentrations.

Fluorescent sodium indicators can be used on a wide variety of tissues, including blood, the brain, muscles, and secretory epithelia in vitro, as well as on plants. Fluorescent techniques are compatible with many analytical systems, including fluorescent microscopes, plate readers, flow cytometers, or even multiphoton techniques. Many experiments that utilize fluorescent indicators, including potassium ion and ATPase studies, aim to determine the spatial and temporal resolution or steady-state changes in sodium concentration.

Additionally, fluorescent techniques can also be used to measure sodium bursts in axons and presynaptic terminals. Sodium benzofuran isophthalate (SBFI), in particular, is a common fluorescent probe used for sodium quantification which exists as an ultraviolet (UV)-excitable, ratiometric green indicator. Ratiometry is optimal for fluorescent imaging because it typically reduces the effects of photobleaching or negative effects of heterogeneous dye loading. SBFI has also widely been shown to accurately detect physiological concentrations of sodium in the presence of potassium and other monovalent cations.

Other, various green fluorescent indicators are commercially available that respond to intracellular sodium ion concentration in the physiological range up to 10 mM. These indicators are small synthetic fluorochromes fused with a sodium binding moiety. They exhibit an increase in green fluorescence emission intensity upon binding to sodium molecules with only a small shift in wavelength.

Datasets:	Application Notes:
Sodium/potassium-transporting ATPase Inhibitors (IC50, Ki) Sodium/calcium exchanger 1 Inhibitors (IC50, Ki)	Fluorimetric detection of ATPase and protein phosphatase activities by monitoring formation of inorganic phosphate

Colorimetric kits

Colorimetric kits are another widely adopted method of detecting sodium ion concentration in biological samples. Colorimetric detection kits are based on the use of sodium ions as cofactors for the enzymatic activity of β-Galactosidase (β-Gal). These assays are quantitative, can use starting samples from saliva, serum or urine, and usually have sensitivity as low as 25 µM. In addition, other biological proteins present within complex samples, including endogenous ions, ascorbic acid, creatinine, glucose, urea, and bilirubin, do not interfere with the reaction.



Typically, kit reagents and standards (β-Gal, dithiothreitol (DTT), the substrate, the sodium developer, and standard) are ready to use as supplied and simply need to be equilibrated to room temperature. Fresh samples are encouraged, and must be diluted in the assay buffer accordingly. Colorimetric sodium detection kits offer a simple two-step protocol, where controls or standards are first added to the wells of a 96-well plate, then β-Gal is added to create hydrolyzed byproducts. Then the substrate is added, and then a sodium developer is added which induces a reaction to create a detectable chromophore. Finally, the plate can be measured at an optical density of 405 nm. Overall, colorimetric kits provide a simple protocol, do not require hazardous reagents, are inexpensive and have quick experimental times for the accurate quantitation of sodium in a complex sample.

Resources:

Dithiothreitol (DTT) (1 M) Preparation and Recipe

Less Common Developing Methodologies

• Paper-Based Colorimetry As colorimetry is cost-effective, reliable, and amenable to visual detection, the fundamentals of these techniques have been used throughout research. Colorimetry using paper-based technology has been of notable importance as it is extremely inexpensive and can be used as a point of care diagnostic platform. This construct offered an easy, nearly instantaneous, visual method of detecting sodium in an eco-friendly, low cost manner, without sophisticated instrumentation.
• Microfluidic Technology Microfluidic analytical devices also offer simple, portable, and inexpensive technologies for many applications in clinical diagnostic, food analysis, and environmental monitoring.
• Nanosensors Recently, engineering efforts have been targeted at the creation of selective and sensitive probes for sodium quantitation, a challenging task due to the obvious interference from other alkali metal ions, particularly potassium. One research focus by Kaur & Kaur (2018) developed fluorescent organic nanoparticles from a Biginelli-based receptor that showed great efficiency, low cost, and high sensitivity. The device offered an excellent fluorescent switch-on sensing technique for the selective monitoring of sodium ions in a physiological range, and additionally showed adequate stability in a highly ionic solution. The practical applicability of the nanosensor was assessed through monitoring sodium concentration in urine, sweat, lake, and tap water samples.
• Chemosensors The pursuit of developing effective, sensitive and economic chemosensors for sodium ion quantitation has embraced current research efforts, owing to the close relation of sodium to human health. Like other detection methods, a key obstacle in designing selective chemosensors lies in the competitive binding tendency of other cations. To overcome this challenge, some chemosensors have been developed with varying structural modifications for the selective detection of sodium ions.

Product Ordering Information

---

References

---

Sodium
Sodium Ion
Colorimetric detection of sodium ion in serum based on the G-quadruplex conformation related DNAzyme activity
Development of a paper printed colorimetric sensor based on Cu-Curcumin nanoparticles for evolving point-of-care clinical diagnosis of sodium
Microfluidic-based ion-selective thermoplastic electrode array for point-of-care detection of potassium and sodium ions
Fluorescent metal ion indicators based on benzoannelated crown systems: a green fluorescent indicator for intracellular sodium ions
Fluorescent sensors for sodium ions
All-solid state ion-selective carbon black-modified printed electrode for sodium detection in sweat
Estimation of sodium ions using easily engineered organic nanoparticles-based turn-on fluorescent sensor: Application in biological and environmental samples
All-solid-state potassium-selective sensor based on carbon black modified thermoplastic electrode
A novel thread-based microfluidic device for capillary electrophoresis with capacitively coupled contactless conductivity detection