A new easy-to-use method for quantification of proteins in solution has been developed. It is based on adsorption competition of the sample protein and fluorescently labeled bovine serum albumin (BSA) onto gold particles. The protein concentration is determined by observing the magnitude of fluorescence altered by quenching the fluorescence on the gold particles in a homogeneous assay format. Under optimal low pH conditions, the assay allowed the determination of picogram quantities (7.0 microg/L) of proteins with an average variation of 4.5% in a 10 min assay. The assay sensitivity was more than 10-fold improved from those of the commonly used most sensitive commercial methods. In addition, the particle sensor provides a simple and rapid assay format without requirements for hazardous test compounds and elevated temperature. Eleven different proteins were tested with the constructed sensor exhibiting a protein-to-protein variability less than 15% allowing protein concentration measurements without the need for recalibration of different proteins.

Persistent luminescence (PeL) materials are used in everyday glow‐in‐the‐dark applications and they show high potential for, e.g., medical imaging, night‐vision surveillance, and enhancement of solar cells. However, the best performing materials contain rare earths and/or other heavy metal and expensive elements such as Ga and Ge, increasing the production costs. Here, (Li,Na)8Al6Si6O24(Cl,S)2:Ti, a heavy‐metal‐ and rare‐earth‐free low‐cost material is presented. It can give white PeL that stays 7 h above the 0.3 mcd m−2 limit and is observable for more than 100 h with a spectrometer. This is a record‐long duration for white PeL and visible PeL without rare earths. The material has great potential to be applied in white light emitting devices (LEDs) combined with self‐sustained night vision using only a single phosphor. The material also exhibits PeL in aqueous suspensions and is capable of showing easily detectable photoluminescence even in nanomolar concentrations, indicating potential for use as a diagnostic marker. Because it is excitable with sunlight, this material is expected to additionally be well‐suited for outdoor applications.

Adsorption of sample protein to Eu(3+) chelate-labeled nanoparticles is the basis of the developed noncompetitive and homogeneous method for the estimation of the protein isoelectric point (pI). The lanthanide ion of the nanoparticle surface-conjugated Eu(3+) chelate is dissociated at a low pH, therefore decreasing the luminescence signal. A nanoparticle-adsorbed sample protein prevents the dissociation of the chelate, leading to a high luminescence signal. The adsorption efficiency of the sample protein is reduced above the isoelectric point due to the decreased electrostatic attraction between the negatively charged protein and the negatively charged particle. Four proteins with isoelectric points ranging from ~5 to 9 were tested to show the performance of the method. These pI values measured with the developed method were close to the theoretical and experimental literature values. The method is sensitive and requires a low analyte concentration of submilligrams per liter, which is nearly 10000 times lower than the concentration required for the traditional isoelectric focusing. Moreover, the method is significantly faster and simpler than the existing methods, as a ready-to-go assay was prepared for the microtiter plate format. This mix-and-measure concept is a highly attractive alternative for routine laboratory work.

A sensitive and rapid assay for the quantification of proteins, based on sample protein adsorption to Eu(3+)-chelate-labeled nanoparticles, was developed. The lanthanide ion of the surface-conjugated Eu(3+) chelate is dissociated at a low pH, decreasing the luminescence signal. The increased concentration of the sample protein prevents dissociation of the chelate, leading to a high luminescence signal due to the nanoparticle-bound protein. The assay sensitivity for the quantification of proteins was 130 pg for bovine serum albumin (BSA), which is an improvement of nearly 100-fold from the most sensitive commercial methods. The average coefficient of variation for the assay of BSA was 8%. The protein-to-protein variability was sufficiently low; the signal values varied within a 28% coefficient of variation for nine different proteins. The developed method is relatively insensitive to the presence of contaminants, such as nonionic detergents commonly found in biological samples. The existing methods tested for the total protein quantification failed to measure protein concentration in the presence of bacterial cell lysate. The developed method quantified protein also in samples containing insoluble cell components reducing the need for additional centrifugal assay steps and making the concept highly attractive for routine laboratory work.

Nanoparticle assay utilizing time-resolved luminescence resonance energy transfer (TR-LRET) was developed for the detection of protein aggregation. This mix-and-measure nanoparticle assay is based on the competitive adsorption of the sample and the acceptor-labeled protein to donor europium(III) polystyrene particles. The protein aggregation was detected with the developed TR-LRET nanoparticle assay, UV240 absorbance and dynamic light scattering (DLS). All methods well equally detected the aggregation and aggregates, whose size ranged from single protein to more than 1000 nm aggregates. The developed method allowed the aggregation detection of the entire size range at more than 10,000 times lower concentration, 30 μg/L, compared to UV240 and DLS. The simple-to-use and sensitive nanoparticle assay with existing microtiter plate luminometric instrumentation can find use as a routine tool for protein aggregation studies in biochemical laboratories and for quality assessment of protein products in industry.