NEPHELOstar Plus

Turbidity is a fairly general concept that is used to describe the dispersion of particulate matter within a liquid phase. Measurement of turbidity is classically important in water quality testing where turbidity is often expressed in NTUs (nephelometric turbidity units). Assessing turbidity is also beneficial in other applications including biological samples where quantifying turbidity is important for measuring bacteria cell growth or antibody precipitation.

NTU values can be derived from a calibrated nephelometer or turbidimeter such as the HACH^® 2100N turbidimeter; however, collecting turbidity data with a turbidimeter is a time consuming, multistep process that employs large sample volumes. Here, we provide a higher throughput, simplified, low volume approach to the collection of NTU data using the NEPHELOstar^® Plus. We present data directly comparing the NEPHELOstar Plus, expressed in RNUs (relative nephelometry units), to the NTU results from a HACH^® turbidimeter.

The precipitation of Ca²⁺ and phosphate results in calcium phosphate that is used for building up bone and teeth. Disregulation of this strictly regulated process may result in cardiovascular diseases. Here, we present a novel assay to determine the intrinsic ability of serum to inhibit calcification. It relies on the formation of small colloidal protein-mineral complexes, so-called primary calciprotein particles (CPP). These are converted into secondary CPPs and the time it takes for conversion reflects the inhibitory calcification propensity of the serum. Secondary CPPs differ from primary CPPs in regard to particle diameter and shape which can be detected by measuring light scattering.

This nephelometric assay was measured on BMG LABTECH's Nephelostar^® Plus in sera of transgenic mice with different propensities to inhibit calcification. These differences were mirrored by differing conversion times of primary to secondary CPPs. Furthermore, different conversion times were determined for hemodialysis patients that have an increased risk in for calcifications.

Nephelometry measures the forward scattered light when passing solutions. This can be used to determine particles in solution as they increase light-scattering. The particles may be derived from drugs at their limit of solubility or from microbes. Hence, determination of drug-solubility and microbial growth are two main applications for nephelometry.

Using a microplate-based nephelometer, the NEPHELOstar^® Plus, solubility of the antifungal substances Econazole-nitrate and ciclopirox-olamine each complexed with Cyclodextrins was monitored and showed a higher solubility than their uncomplexed form. The Cyclodextrin-complexes were studied regarding their antifungal activity on Candida albicans and revealed a higher efficiency of the Econazole complex as compared to the ciclopirox complex.

This study has proven that laser nephelometry in a 96-well microtiter plate can be used as a method for the rapid determination of the solubility of potential drug compounds.

Rheumatoid Factors (RF) are immunoglobulins which react to antigenic sites on the Fc region of human or animal immunoglobulin G (IgG). Presence of RF is one of the classification criteria for RA and presence of RF is associated with a poorer prognosis such as increased risk of developing erosive disease.

A method of measuring RF uses nephelometry. Patient serum is added to a microplate containing a fixed amount of antigen (IgG). Any RF present will form an antibody-antigen complex with the IgG and the concentration of the RF antibody can be determined by light dispersion. The microplate-based nephelometry reader, the NEPHELOstar^® Plus, enables the assay and, hence, provides the advantage of higher throughput, low sample volumes and cost-effectiveness.

Nephelometry is a direct method of measuring light scattered by particles suspended in solution at right angles to the beam, or preferably, at a forward angle. In dilute solutions, where absorption and reflection are minimal, the intensity of the scattered light is a function of the concentration of scattering particles such as microbes.

In this application note, the only laser-based microplate nephelometer was used to monitor growth of the Corynebacterium glutamicum. Relative nephelometric units detected by the NEPHELOstar^® Plus were compared to OD600 absorbance measurements and revealed that both density measurements correlated well, with nephelometry being the more sensitive method.