Enhanced immunoassay sensitivity using chemiluminescent acridinium esters with increased light output

Development of a fully automated chemiluminescent immunoassay for the quantitative and qualitative detection of antibodies against African swine fever virus p72

African swine fever (ASF), caused by ASF virus (ASFV), is a highly infectious and severe hemorrhagic disease of pigs that causes major economic losses. Currently, no commercial vaccine is available and prevention and control of ASF relies mainly on early diagnosis. Here, a novel automated double antigen sandwich chemiluminescent immunoassay (DAgS-aCLIA) was developed to detect antibodies against ASFV p72 (p72-Ab). For this purpose, recombinant p72 trimer was produced, coupled to magnetic particles as carriers and labeled with acridinium ester as a signal trace. Finally, p72-Ab can be sensitively and rapidly measured on an automated chemiluminescent instrument. For quantitative analysis, a calibration curve was established with a laudable linearity range of 0.21 to 212.0 ng/mL (R2 = 0.9910) and a lower detection limit of 0.15 ng/mL. For qualitative analysis, a cut-off value was set at 1.50 ng/mL with a diagnostic sensitivity of 100.00% and specificity of 98.33%. Furthermore, antibody response to an ASF gene-deleted vaccine candidate can be accurately quantified using this DAgS-aCLIA, as evidenced by early seroconversion as early as 7 days post-immunization and high antibody levels. Compared with available enzyme-linked immunosorbent assays, this DAgS-aCLIA demonstrated a wider linearity range of 4 to 16-fold, and excellent analytical sensitivity and agreement of over 95.60%. In conclusion, our proposed DAgS-aCLIA would be an effective tool to support ASF epidemiological surveillance.IMPORTANCEAfrican swine fever virus (ASFV) is highly contagious in wild boar and domestic pigs. There is currently no vaccine available for ASF, so serological testing is an important diagnostic tool. Traditional enzyme-linked immunosorbent assays provide only qualitative results and are time and resource consuming. This study will develop an automated chemiluminescent immunoassay (CLIA) that can quantitatively and qualitatively detect antibodies to ASFV p72, greatly reducing detection time and labour-intensive operation, and improving detection sensitivity and linearity range. This novel CLIA would serve as a reliable and convenient tool for ASF pandemic surveillance and vaccine development.

Enhancing the photocatalytic upcycling of polystyrene to benzoic acid: a combined computational-experimental approach for acridinium catalyst design

Converting polystyrene into value-added oxygenated aromatic compounds is an attractive end-of-life upcycling strategy. However, identification of appropriate catalysts often involves laborious and time-consuming empirical screening. Herein, after demonstrating the feasibility of using acridinium salts for upcycling polystyrene into benzoic acid by photoredox catalysis for the first time, we applied low-cost descriptor-based combinatorial in silico screening to predict the photocatalytic performance of a family of potential candidates. Through this approach, we identified a non-intuitive fluorinated acridinium catalyst that outperforms other candidates for converting polystyrene to benzoic acid in useful yields at low catalyst loadings (≤5 mol%). In addition, this catalyst also proved effective with real-life polystyrene waste containing dyes and additives. Our study underscores the potential of computer-aided catalyst design for valorizing polymeric waste into essential chemical feedstock for a more sustainable future.

Rapid Antigen Diagnostics as Frontline Testing in the COVID‐19 Pandemic

The ongoing global COVID‐19 pandemic, caused by the SARS‐CoV‐2 virus, has resulted in significant loss of life since December 2019. Timely and precise virus detection has been proven as an effective solution to reduce the spread of the virus and to track the epidemic. Rapid antigen diagnostics has played a significant role in the frontline of COVID‐19 testing because of its convenience, low cost, and high accuracy. Herein, different types of recently innovated in‐lab and commercial antigen diagnostic technologies with emphasis on the strengths and limitations of these technologies including the limit of detection, sensitivity, specificity, affordability, and usability are systematically reviewed. The perspectives of assay development are looked into.

Solvent effect on chemiluminescence of acridinium thioester: a computational study

Chemiluminescent labelling, which is one of the promising procedures of modern immunodiagnostics, is increasingly carried out using acridinium derivatives, oxidant and alkaline aqueous environment. However, the efficiency of chemiluminescence of luminol or acridinium esters is higher in non-aqueous solvents such as DMSO or acetonitrile. Therefore, the search for a new environment of chemiluminescence reaction, especially this characterized by the higher quantum yield of chemiluminescence, is one of the aims of the research undertaken. Using computational methods (DFT and TD DFT with PCM model of solvent), we examined thermodynamic and kinetic data concerning the chemiluminescence and competitive dark pathways. Our results suggest that better characteristics of chemiluminescence reaction of acridinium thioester are observed in nonpolar solvents, such as methylcyclohexane, n-hexane and n-pentane, than in aqueous media used so far. Further experimental verification is necessary to confirm the possible application of proposed nonpolar solvents in chemiluminescent labelling and hence in immunodiagnostics.

Type of serum collection tube does not impact neurofilament light chain levels

Blood neurofilament light chain (NfL) has been reported to be a promising biomarker of neurological disease. NfL is predominantly measured in serum (sNfL), but there is a lack of reports regarding the effects of collection tubes on sNfL levels. We assessed sNfL levels using a novel immunoassay in 18 participants using 3 different types of serum collection tubes (no additive, with silica clot activator, and serum separator tubes). Variation observed in sNfL levels between samples from different collection tubes was similar to that observed in duplicate runs from the same tube. These findings support a lack of effect of type of serum collection tube on sNfL levels.

Development and multicenter performance evaluation of fully automated SARS-CoV-2 IgM and IgG immunoassays

Objectives

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has rapidly spread globally. The laboratory diagnosis of SARS-CoV-2 infection has relied on nucleic acid testing; however, it has some limitations, such as low throughput and high rates of false negatives. Tests of higher sensitivity are needed to effectively identify infected patients.

Methods

This study has developed fully automated chemiluminescent immunoassays to determine IgM and IgG antibodies to SARS-CoV-2 in human serum. The assay performance has been evaluated at 10 hospitals. Clinical specificity was evaluated by measuring 972 hospitalized patients and 586 donors of a normal population. Clinical sensitivity was assessed on 513 confirmed cases of SARS-CoV-2 by RT-PCR.

Results

The assays demonstrated satisfied assay precision with coefficient of variation of less than 4.45%. Inactivation of specimen did not affect assay measurement. SARS-CoV-2 IgM showed clinical specificity of 97.33 and 99.49% for hospitalized patients and the normal population respectively, and SARS-CoV-2 IgG showed clinical specificity of 97.43 and 99.15% respectively. SARS-CoV-2 IgM showed clinical sensitivity of 82.54, 92.93, and 84.62% before 7 days, 7-14 days, and after 14 days respectively, since onset of symptoms, and SARS-CoV-2 IgG showed clinical sensitivity of 80.95, 97.98, and 99.15% respectively at the same time points above.

Conclusions

We have developed fully automated immunoassays for detecting SARS-CoV-2 IgM and IgG antibodies in human serum. The assays demonstrated high clinical specificity and sensitivity, and add great value to nucleic acid testing in fighting against the global pandemic of the SARS-CoV-2 infection.

Computational Insights on the Mechanism of the Chemiluminescence Reaction of New Group of Chemiluminogens-10-Methyl-9-thiophenoxycarbonylacridinium Cations

Immunodiagnostics, in which one of the promising procedures is the chemiluminescent labelling, is essential to facilitate the detection of infections in a human organism. One of the standards commonly used in luminometric assays is luminol, which characterized by low quantum yield in aqueous environments. Acridinium esters have better characteristics in this topic. Therefore, the search for new derivatives, especially those characterized by the higher quantum yield of chemiluminescence, is one of the aims of the research undertaken. Using the proposed mechanism of chemiluminescence, we examined the effect of replacing a single atom within a center of reaction on the efficient transformation of substrates into electronically excited products. The density functional theory (DFT) and time dependent (TD) DFT calculated thermodynamic and kinetic data concerning the chemiluminescence and competitive dark pathways suggests that some of the scrutinized derivatives have better characteristics than the chemiluminogens used so far. Synthesis of these candidates for efficient chemiluminogens, followed by studies of their chemiluminescent properties, and ultimately in chemiluminescent labelling, are further steps to confirm their potential applicability in immunodiagnostics.

Ultrasound-Enhanced Chemiluminescence for Bioimaging

Tissue imaging has emerged as an important aspect of theragnosis. It is essential not only to evaluate the degree of the disease and thus provide appropriate treatments, but also to monitor the delivery of administered drugs and the subsequent recovery of target tissues. Several techniques including magnetic resonance imaging (MRI), computational tomography (CT), acoustic tomography (AT), biofluorescence (BF) and chemiluminescence (CL), have been developed to reconstruct three-dimensional images of tissues. While imaging has been achieved with adequate spatial resolution for shallow depths, challenges still remain for imaging deep tissues. Energy loss is usually observed when using a magnetic field or traditional ultrasound (US), which leads to a need for more powerful energy input. This may subsequently result in tissue damage. CT requires exposure to radiation and a high dose of contrast agent to be administered for imaging. The BF technique, meanwhile, is affected by strong scattering of light and autofluorescence of tissues. The CL is a more selective and sensitive method as stable luminophores are produced from physiochemical reactions, e.g. with reactive oxygen species. Development of near infrared-emitting luminophores also bring potential for application of CL in deep tissues and whole animal studies. However, traditional CL imaging requires an enhancer to increase the intensity of low-level light emissions, while reducing the scattering of emitted light through turbid tissue environment. There has been interest in the use of focused ultrasound (FUS), which can allow acoustic waves to propagate within tissues and modulate chemiluminescence signals. While light scattering is decreased, the spatial resolution is increased with the assistance of US. In this review, chemiluminescence detection in deep tissues with assistance of FUS will be highlighted to discuss its potential in deep tissue imaging.

Determination of parvovirus antibodies in canine serum using magnetic bead-based chemiluminescence immunoassay

Canine parvovirus type 2 (CPV-2), as a highly contagious and potentially fatal disease of dogs and many other carnivores, usually causes severe gastroenteritis and myocarditis. Therefore, it is very necessary and urgent to have an accurate method to determine the CPV-2 antibodies (CPV-2-Ab) in canine samples. Here, a magnetic bead-based chemiluminescence immunoassay was established and optimized to detect the concentration of CPV-2-Ab in serum. And a commercial assay was also used to evaluate the consistency with our method. After optimization of the detective system, the CPV-2-Ab was captured by CPV-antigen-magnetic bead (8.3 µg/mL); then combined with the conjugation of anti-canine IgG antibody-acridinium ester (0.36 µg/mL). Finally, collected the signal (read the luminosity) after 1 H reaction time. The linear correlation coefficient (R² ) is 0.9924. The limit of detection (sensitivity) is 0.36 ng/mL (the linear dynamic range: 1.32-93.75 ng/mL), and the average recovery is 100.89% without cross-reactions with other canine viral antibodies. The results' correlation between commercial assays and this method is 0.9888. This immunoassay establishes that it has high sensitivity, accuracy, and specificity in clinical analysis, indicating that this method could be suitable for quantitative detection of CPV-2-Ab and evaluation of vaccination effect.

A full-automated magnetic particle-based chemiluminescence immunoassay for rapid detection of cortisol in milk

A sensitive full-automated micromagnetic particles (MMPs) based competitive chemiluminescent immunoassay (CLIA) was developed to detect cortisol in milk. Polyclonal antibody (pAb) with good specificity against cortisol was produced. The antigen (cortisol-OVA) was labeled with acridinium ester (cortisol-OVA-AE) as signal tracer. During the detection, the free cortisol in sample will compete with cortisol-OVA-AE for binding to pAb. To capture pAb, MMPs conjugated with goat anti-rabbit IgG was added. The whole immunoassay process (exclude sample pretreatment) was performed by automatic chemiluminescence immunoassay instrument, which could consume less test time (within 40 min) and avoid error from manual operation. The method showed a good detection limit of 0.12 ng/mL, a broad linear range from 0.42 to 72.27 ng/mL for cortisol detection, negligible cross-reactivity with related analogues and satisfied recovery (84.3%-102.3%) for spiked milk samples test. Simultaneously, since the results of proposed method had no significant difference with those of LC-MS/MS, the proposed method was confirmed to have a potential applicability for rapidly monitoring cortisol in the food.

Lectin-carbohydrate complex evaluation by chemiluminescence

In order to characterize the affinity between specific carbohydrate-binding proteins such as lectins, a model is proposed to study these interactions using a polysaccharide membrane to simulate such adsorption. Here, lectin-carbohydrate interactions were chemiluminescently investigated using lectins conjugated to acridinium ester (AE) and polysaccharides composed of their respective specific carbohydrates. The lectin-AE conjugates were incubated with discs (0.0314-0.6358 cm²) of phytagel, chitosan and carrageenan. The complex formation chemiluminescently detected followed the Langmuir isotherm from which constants were estimated. The association constant (K_a) and maximum binding sites on the membranes were 2.4 × 10^-7 M^-1 ± 0.8 × 10^-7 M^-1 and 1.3 × 10^-3 mol. mg^-1 ± 0.3 × 10^-3 mol. mg^-1 (Con A); 0.9 × 10^-6 M^-1 ± 0.4 × 10^-6 M^-1 and 0.021 × 10^-3 mol. mg^-1 ± 0.003 × 10^-3 mol. mg^-1 (WGA) and 2.0 × 10^-6 M^-1 ± 0.9 × 10^-6 M^-1 and 0.069 × 10^-3 mol. mg^-1 ± 0.010 × 10^-3 mol. mg^-1 (PNA). The proposed model might be useful to study binding affinity and estimate the amount of binding not limited by the sugar content in the membrane.

miRNA assays in the clinical laboratory: workflow, detection technologies and automation aspects

microRNAs (miRNAs) are short non-coding RNA molecules that regulate gene expression in eukaryotes. Their differential abundance is indicative or even causative for a variety of pathological processes including cancer or cardiovascular disorders. Due to their important biological function, miRNAs represent a promising class of novel biomarkers that may be used to diagnose life-threatening diseases, and to monitor disease progression. Further, they may guide treatment selection or dosage of drugs. miRNAs from blood or derived fractions are particularly interesting candidates for routine laboratory applications, as they can be measured in most clinical laboratories already today. This assures a good accessibility of respective tests. Albeit their great potential, miRNA-based diagnostic tests have not made their way yet into the clinical routine, and hence no standardized workflows have been established to measure miRNAs for patients' benefit. In this review we summarize the detection technologies and workflow options that exist to measure miRNAs, and we describe the advantages and disadvantages of each of these options. Moreover, we also provide a perspective on data analysis aspects that are vital for translation of raw data into actionable diagnostic test results.

Acridinium Ester-Functionalized Carbon Nanomaterials: General Synthesis Strategy and Outstanding Chemiluminescence

In this work, three different kinds of acridinium ester (AE)-functionalized carbon nanomaterials, including AE-functionalized carbon nanoparticles (AE-CNPs), AE-functionalized graphene oxide (AE-GO), and AE-functionalized multiwalled carbon nanotubes (AE-MCNTs), were synthesized for the first time via a simple, general, and noncovalent strategy. AE molecules were assembled on the surface of carbon nanomaterials by electrostatic interaction, π-π stacking interaction, and amide bond. The synthesized AE-CNPs, AE-GO, and AE-MCNTs with 5.0 × 10(-8) mol·L(-1) of synthetic AE concentration, which was very low compared with other chemiluminescence (CL) reagents such as luminol, N-(aminobutyl)-N-(ethylisoluminol), and lucigenin at the concentration of 3.3 × 10(-4) to 5.0 × 10(-6) mol·L(-1) used for the synthesis of CL-functionalized nanomaterials, exhibited outstanding CL activity and good stability. It was found that carbon nanomaterials as nanosized platforms could efficiently immobilize AE molecules and facilitate the formation of OH(•) and O2(•-), leading to strong light emission. Moreover, the CL intensity of AE-GO was the highest, which was about 8.7 and 3.7 times higher than that of AE-CNPs and AE-MCNTs, respectively. This mainly resulted from a difference in the amount of adsorbed AE molecules on the surface of different carbon nanomaterials. Additionally, the prepared AE-CNPs demonstrated excitation-dependent fluorescence property and good fluorescence stability against photobleaching. On the basis of the excellent CL and special fluorescence properties of AE-CNPs, a dual-mode array strategy has been proposed for the first time and seven kinds of transition-metal ions could be successfully discriminated.

Effective chemiluminogenic systems based on acridinium esters bearing substituents of various electronic and steric properties

A series of new acridinium esters, variously substituted in the benzene ring, have been investigated for the mechanism of light generation and ability to show chemiluminescence in various environments.

A comparison of chemiluminescent acridinium dimethylphenyl ester labels with different conjugation sites

Chemiluminescent acridinium dimethylphenyl esters are highly sensitive labels that are used in automated assays for clinical diagnosis. Light emission from these labels and their conjugates is triggered by treatment with alkaline peroxide. Conjugation of acridinium ester labels is normally done at the phenol. During the chemiluminescent reaction of these acridinium esters, the phenolic ester is cleaved and the light emitting acridone moiety is liberated from its conjugate partner. In the current study, we report the synthesis of three new acridinium esters with conjugation sites at the acridinium nitrogen and compare their properties with that of a conventional acridinium ester with a conjugation site at the phenol. Our study is the first that provides a direct comparison of the emissive properties of acridinium dimethylphenyl esters (free labels and protein conjugates) with different conjugation sites, one where the light emitting acridone remains attached to its conjugate partner versus conventional labeling which results in cleavage of the acridone from the conjugate. Our results indicate that the conjugation at the acridinium nitrogen, which also alters how the acridinium ring and phenol are oriented with respect to the protein surface, has a minimal impact on emission kinetics and emission spectra. However, this mode of conjugation to three different proteins led to a significant increase in light yield which should be useful for improving the assay sensitivity.

Multiplexed detection of two proteins by a reaction kinetics-resolved chemiluminescence immunoassay strategy

A multiplexed immunoassay method was proposed for the sequential detection of two proteins based on a novel chemiluminescence reaction kinetics-resolved strategy.

Synthesis and properties of chemiluminescent acridinium esters with different N-alkyl groups

Acridinium esters containingN-alkyl groups with charge-neutral sulfobetaine zwitterions when compared toN-sulfopropyl groups exhibit faster light emission, improved chemiluminescence stability and lower non-specific binding.

Synthesis and properties of chemiluminescent acridinium ester labels with fluorous tags

Acridinium dimethylphenyl esters are highly sensitive chemiluminescent labels that are used in clinical diagnostics. Light emission from these labels is triggered with alkaline peroxide in the presence of the cationic surfactant cetyltrimethylammonium chloride (CTAC). CTAC compresses emission times of these labels to <5 seconds and also increases overall light yield 3-4 fold. The observed enhancement in acridinium ester chemiluminescence (light yield) is quite sensitive to the polarity of the micellar interface. In the current study, we report the synthesis of new acridinium ester labels with fluorous tags of varying fluorine content and their chemiluminescence in the presence of cationic micelles of CTAC, anionic micelles of sodium perfluorooctanoate (SPFO) as well as mixed micelles of CTAC and SPFO. These studies indicate that in the presence of the mixed micelle system of CTAC and SPFO and at low mole fractions of SPFO, polarity of the mixed micelle interface is lower than that of CTAC leading to a greater enhancement of chemiluminescence for both fluorinated acridinium esters as well as a structurally analogous but non-fluorinated acridinium ester. Chemiluminescence stability of the fluorinated acridinium esters was either comparable to or better than the stability of the non-fluorinated acridinium ester. Non-specific binding to paramagnetic microparticles was higher for fluorinated acridinium esters requiring a surfactant wash to reduce their non-specific binding to the same extent as that observed for the non-fluorinated acridinium ester.

Chemiluminescence accompanied by the reaction of acridinium ester and manganese (II)

An acridinium ester (AE) alkaline solution can react with Mn(II) to generate a strong chemiluminescence (CL) centered at 435 nm. The effects of reaction conditions such as pH and Mn(II) concentration on CL intensity were examined. In order to explore the CL mechanism, the effect of oxygen on the CL reaction was examined and an X-ray photoelectron spectroscopy study of the reaction precipitate was carried out. The results indicated that oxygen participated in the CL reaction and Mn(IV) was the primary product in the system. A possible mechanism was proposed that involved two pathways: (1) dissolved oxygen was reduced to reactive oxygen radicals by Mn(II), these reactive intermediates then reacted with AE to produce excited state acridone; (2) Mn(II) could reduce AE to partly reduced AE, which then reacted with oxygen to form excited state acridone. The reactions of other metal ions with AE were also tested, and only Mn(II) was shown to trigger strong CL emission of AE, which indicated that the system had good selectivity for Mn(II).

Effect of branching in remote substituents on light emission and stability of chemiluminescent acridinium esters

Acridinium dimethylphenyl esters are widely used as chemiluminescent labels in automated immunoassays for clinical diagnostics in Siemens Healthcare Diagnostics' ADVIA Centaur® systems.

Glycophenotype evaluation in cutaneous tumors using lectins labeled with acridinium ester

Background. Tumor cells show alterations in their glycosylation patterns when compared to normal cells. Lectins can be used to evaluate these glycocode changes. Chemiluminescence assay is an effective technique for quantitative analysis of proteins, nucleic acids, and carbohydrates due to its high sensitivity, specificity, and rapid testing. Objective. To use histochemiluminescence based on lectin conjugated to acridinium ester (AE) for the investigation of glycophenotype changes in cutaneous tumors. Methods. Concanavalin A (Con A), Peanut agglutinin (PNA), Ulex europaeus agglutinin-I (UEA-I), and Maackia amurensis agglutinin (MAA) were conjugated to acridinium ester. Biopsies of cutaneous tumors and normal skin were incubated with the lectins-AE, and chemiluminescence was quantified and expressed as Relative Light Units (RLU). Results. Actinic keratosis (AK), keratoacanthoma (KA), squamous cell carcinoma (SCC), and basal cell carcinoma (BCC) showed lower expression of α-D-glucose/mannose and α-L-fucose residues compared to normal tissue. Cutaneous tumors displayed higher expression of Gal-β(1-3)-GalNAc residues than normal tissue. AK and SCC exhibited higher expression of Neu5Ac-α(2,3)Gal residues than normal epidermis. KA and BCC showed equivalent RLU values compared to normal tissue. Conclusions. Lectin histochemiluminescence allowed quantitative assessment of the carbohydrate expression in cutaneous tissues, contributing to eliminate the subjectivity of conventional techniques used in the histopathological diagnosis.

Synthesis and properties of differently charged chemiluminescent acridinium ester labels

Chemiluminescent acridinium dimethylphenyl esters containing N-sulfopropyl groups in the acridinium ring are highly sensitive, hydrophilic labels that are used in automated immunoassays for clinical diagnostics. Light emission from these labels is triggered with alkaline peroxide in the presence of a cationic surfactant. At physiological pH, N-sulfopropyl acridinium esters exist as water adducts that are commonly referred to as pseudobases. Pseudobase formation, which results from addition of water to the zwitterionic N-sulfopropyl acridinium ring, neutralizes the positive charge on the acridinium nitrogen and imparts a net negative charge to the label due to the sulfonate moiety. As a consequence, N-sulfopropyl acridinium ester conjugates of small molecule haptens as well as large molecules such as proteins gain negative charges at neutral pH. In the current study, we describe the synthesis and properties of two new hydrophilic acridinium dimethylphenyl ester labels where the net charge in the labels was altered. In one label, the structure of the hydrophilic N-alkyl group attached to the acridinium ring was changed so that the pseudobase of the label contains no net charge. In the second acridinium ester, two additional negative charges in the form of sulfopropyl groups were added to the acridinium ring to make this label's pseudobase strongly anionic. Chemiluminescence measurements of these labels, as well as their conjugates of an antibody with a neutral pI, indicate that acridinium ester charge while having a modest effect on emission kinetics has little influence on light output. However, our results demonstrate that acridinium ester charge can affect protein pI, apparent chemiluminescence stability and non-specific binding of protein conjugates to microparticles. These results emphasize the need for careful consideration of acridinium ester charge in order to optimize reagent stability and performance in immunoassays. In the current study, we observed that for a neutral protein, an acridinium ester with a hydrophilic but charge-neutral N-alkyl group afforded faster light emission, lower non-specific binding and better chemiluminescence stability than an analogous label with an anionic N-alkyl group.

Zwitterionic reagents for labeling, cross-linking and improving the performance of chemiluminescent immunoassays

Improving reagent performance in immunoassays both to enhance assay sensitivity and to minimize interference are ongoing challenges in clinical diagnostics. We describe herein the syntheses of a new class of hydrophilic reagents containing sulfobetaine zwitterions and their applications. These zwitterionic reagents are potentially useful for improving the properties of immunoassay reagents. We demonstrate for the first time that zwitterion labeling is a general and viable strategy for reducing the non-specific binding of proteins to microparticles and, to improve the aqueous solubility of hydrophobic peptides. We also describe the synthesis of zwitterionic cross-linking reagents and demonstrate their utility for peptide conjugation. In automated, chemiluminescent immunoassays, improved assay performance was observed for a hydrophobic, small analyte (theophylline) using an acridinium ester conjugate with a zwitterionic sulfobetaine linker compared to a hexa(ethylene)glycol linker. Sandwich assay performance for a large analyte (thyroid stimulating hormone) was similar for the two acridinium ester labels. These results indicate that zwitterions are complementary to poly(ethylene)glycol in improving the aqueous solubility and reducing the non-specific binding of chemiluminescent acridinium ester conjugates.

Analytical chemiluminescence and bioluminescence: latest achievements and new horizons

Chemiluminescence (CL) and bioluminescence (BL) are the detection techniques of choice for the development of highly sensitive analytical methods, from immunoassays and nucleic acid hybridization assays to whole-cell biosensors. Nevertheless, basic and applied research on CL and BL aimed at further improving their analytical performance is still very active. This research covers diverse and complementary fields, including (among others) enhancing the light emission efficiency of CL systems, the use of nanomaterials to catalyze or enhance CL/BL reactions, the study of BL proteins to elucidate the color modulation mechanism, the discovery of new BL systems, the production of thermostable BL protein mutants with altered emission spectra, the development of BL imaging techniques to expand our understanding of living systems, and the implementation of CL/BL detection in miniaturized analytical devices. In the near future, we expect even greater diffusion of CL/BL-based analytical methods, especially in portable analytical devices intended for applications ranging from environmental analysis to companion diagnostics for personalized medicine.

9-(2,6-Dimethyl-phen-oxy-carbon-yl)-10-methyl-acridinium trifluoro-methane-sulfonate

In the crystal structure of the title compound, C₂₃H₂₀NO₂⁺·CF₃SO₃⁻, adjacent cations are linked through a network of C—H⋯π and π–π inter­actions, and neighboring cations and anions via C—H⋯O inter­actions. The acridine and benzene ring systems are oriented at a dihedral angle of 31.4 (1)°. The carboxyl group is twisted at an angle of 66.3 (1)° relative to the acridine skeleton. The mean planes of the adjacent acridine moieties are parallel in the crystal structure.

10-Methyl-9-[2-(propan-2-yl)phenoxy-carbonyl]-acridinium trifluoro-methane-sulfonate

In the crystal of the title compound, C₂₄H₂₂NO₂⁺·CF₃SO₃⁻, adjacent cations and anions are connected through C—H⋯O, C—H⋯F and S–O⋯π inter­actions, while neighboring cations via π–π inter­actions [centroid–centroid distance = 3.962 (2) Å]. The acridine and benzene ring systems are oriented at a dihedral angle of 14.6 (1)°. The carboxyl group is twisted at an angle of 87.6 (1)° relative to the acridine skeleton. The mean planes of adjacent acridine units are parallel or inclined at an angle of 13.4 (1)° in the crystal structure.