Silica-Supported Nitrogen-Enriched Porous Benzimidazole-Linked and Triazine-Based Polymers for the Adsorption of CO2.

Two crystalline and five amorphous benzimidazole polymers (BINP) were synthesized and conjugated to porous silica via amine and aldehyde-based materials by a simple reflux procedure. The resulting polymers were subject to thermal analysis for monitoring and quantification of the adsorption and desorption of CO2. All the polymers were capable of adsorbing CO2 from a flowing stream of only 80 mL/min at 25 °C. The adsorbed CO2 onto the polymers were effectively desorbed at room temperature, illustrating the potential application of such polymers for repeated adsorption/desorption of CO2. The CO2 adsorption capacities of these polymers were dependent upon their nitrogen content, specific surface area, and pore size. The available nitrogen atoms for binding to the carbon of CO2 via tetrel bonds also plays an important role in the capture of this gas. Minimal and much lower CO2 adsorption was also noted with two crystalline polymers, compared to the five amorphous counterparts. Intermolecular hydrogen bonding and π-π interaction effectively prevented the polymer N sites of the crystalline polymers from interacting with polarized CO2 molecules.

Electrochemical sensing of histamine using a glassy carbon electrode modified with multiwalled carbon nanotubes decorated with Ag-Ag2O nanoparticles.

A glassy carbon electrode (GCE) was modified with a nanocomposite consisting of multiwalled carbon nanotubes (MWCNTs) loaded with silver-argentous oxide nanoparticles (Ag-Ag2O). The electrode is shown as a viable tool for sensing histamine using differential pulse voltammetry (DPV). The modified GCE, best operated at a potential of 0.97 V (vs. Ag/AgCl) shows higher electrocatalytic activity compared to GCEs modified with MWCNTs or Ag-Ag2O only. Under the optimum conditions, the detection limit is 2 µg⋅L-1 (0.18 µM) and the response is linear in the 5 mg⋅L-1 to 200 mg⋅L-1 histamine concentration range. Sodium chloride, putrescine and cadaverine, commonly present in biological samples and foods, do not interfere. Other performance features include good recoveries, fabrication reproducibility and operational/storage stability. The modified GCE was applied for determination of histamine in fish sauce samples. Graphical abstract A glassy carbon modified with a thin Ag-Ag2O layer decorated on MWCNTs exhibits an enhanced surface area, increasing catalyst interface, and reduced overpotential towards histamine.

Silver-doped CdS quantum dots incorporated into chitosan-coated cellulose as a colorimetric paper test stripe for mercury.

Silver-doped CdS quantum dots capped with mercaptoacetic acid were incorporated into a chitosan-coated filter paper to fabricate a colorimetric test stripe for mercury. Chitosan assisted in the stabilization of CdSAg QDs on cellulose and enhanced the analyte diffusion in the test stripe. Hg(II) ions were captured by mercaptoacetic acid on CdSAg, resulting in a visualized color change from yellow to deep brown. For enhanced sensitivity and quantitation with good reproducibility, the color intensity was recorded, transmitted to a smartphone camera and computed by the ImageJ software to provide a digital readout. The assay was rapid, simple, and selective for mercury as several potential interfering species provoked no signal response. The applicability of the sensing approach was demonstrated for the analysis of spiked Hg(II) ions in cosmetic cream with a detection limit of 124 µM. Graphical abstract Schematic of a colorimetric test stripe consisting of silver-doped CdS quantum dots coated withmercaptoacetic acid and embedded into a chitosan matrix on paper. It enables mercury(II) to be visuallyquantified even in complex matrices such as cosmetics.

Synthesis and electrochemical detection of a thiazolyl-indole natural product isolated from the nosocomial pathogen Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen, capable of surviving in a broad range of natural environments and quickly acquiring resistance. It is associated with hospital-acquired infections, particularly in patients with compromised immunity, and is the primary cause of morbidity and mortality in cystic fibrosis (CF) patients. P. aeruginosa is also of nosocomial importance on dairy farms and veterinary hospitals, where it is a key morbidity factor in bovine mastitis. P. aeruginosa uses a cell-cell communication system consisting of signalling molecules to coordinate bacterial secondary metabolites, biofilm formation, and virulence. Simple and sensitive methods for the detection of biomolecules as indicators of P. aeruginosa infection would be of great clinical importance. Here, we report the synthesis of the P. aeruginosa natural product, barakacin, which was recently isolated from the bovine ruminal strain ZIO. A simple and sensitive electrochemical method was used for barakacin detection using a boron-doped diamond (BDD) and glassy carbon (GC) electrodes, based on cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The influence of electrolyte pH on the peak potential and peak currents was also investigated. At pH 2.0, the peak current was linearly dependent on barakacin concentration (in the range used, 1-10 µM), with correlation coefficients greater than 0.98 on both electrodes. The detection limit (S/N = 3) on the BDD electrode was 100-fold lower than that obtained on the GC electrode. The optimized method using the BDD electrode was extended to bovine (cow feces) and human (sputum of a CF patient) samples. Spiked barakacin was easily detected in these matrices at a limit of 0.5 and 0.05 µM, respectively. Graphical abstract Electrochemical detection of barakacin.

Hairpin DNA as a biobarcode modified on gold nanoparticles for electrochemical DNA detection.

Hairpin DNA (hpDNA) as a novel biobarcode was conjugated with gold nanoparticles (AuNPs) and a reporter DNA (rpDNA) to form hpDNA/AuNP/rpDNA nanoparticles for the detection of an oligonucleotide sequence associated with Helicobacter pylori as a model target. The rpDNA is complementary to about a half-portion of the target DNA sequence (tDNA). A capture DNA probe (cpDNA), complementary to the other half of the tDNA, was immobilized on the surface of a gold electrode. In the presence of tDNA, a sandwich structure of (hpDNA/AuNP/rpDNA)/tDNA/cpDNA was formed on the electrode surface. The differential pulse voltammetry (DPV) detection was based on [Ru(NH3)5(3-(2-phenanthren-9-yl-vinyl)-pyridine)](2+), an electroactive complex that binds to the sandwich structure by its intercalation with the hpDNA and the double-stranded DNA (dsDNA) of the sandwich structure. The several factors--high density of biobarcode hpDNA on the surface of AuNPs, multiple electroactive complex molecules intercalated with each hpDNA and dsDNA molecule, and the intercalation binding mode of the electroactive complex with the DNA sandwich structure--contribute to the DNA sensor with highly selective and sensitive sensing properties. The DNA sensor exhibited a detection limit of 1 × 10(-15) M (i.e., 1 fM), the DNA levels in physiological samples, with linearity down to 2 × 10(-15) M. It can differentiate even one single mismatched DNA from the complementary tDNA. This novel biobarcode-based DNA sensing approach should provide a general platform for development of direct, simple, repetitive, sensitive, and selective DNA sensors for various important applications in analytical, environmental, and clinical chemistry.

Direct electron transfer of glucose oxidase-boron doped diamond interface: a new solution for a classical problem.

A planar boron-doped diamond (BDD) electrode was treated with KOH and functionalized with 3-aminopropyltriethoxysilane (APTES) to serve as a biosensing platform for biomolecule immobilization with glucose oxidase (GOx) as a test model. The free amino groups of GOx and APTES were cross-linked by glutaraldehyde (X), a bifunctional chemical to form a stable enzyme layer (GOx-X-APTES) on BDD. Micrographs obtained by scanning electron microscopy revealed that a mesoporous structure uniformly covered the BDD surface. Cyclic voltammetry of GOx immobilized showed a pair of well-defined redox peaks in neutral phosphate buffer solution, corresponding to the direct electron transfer of GOx. The apparent heterogeneous electron transfer rate constant of the immobilized GOx was estimated to be 8.85 ± 0.47 s(-1), considerably higher than the literature reported values. The determination of glucose was carried out by amperometry at -0.40 V, and the developed biosensor showed good reproducibility and stability with a detection limit of 20 µM. Both ascorbic and uric acids at normal physiological conditions did not provoke any signals. The dynamic range of glucose detection was further extended by covering the enzyme electrode with a thin Nafion layer. The Nafion/GOx-X-APTES/BDD biosensor showed excellent stability, a detection limit of 30 µM, a linear range between 35 µM and 8 mM, and a dynamic range up to 14 mM. Such analytical performances were compared favorably with other complicated sensing schemes using nanomaterials, redox polymers, and nanowires. The APTES-functionalized BDD could be easily extended to immobilize other redox enzymes or proteins of interests.

One-step kinetics-based immunoassay for the highly sensitive detection of C-reactive protein in less than 30 min.

This article reveals a rapid sandwich enzyme-linked immunosorbent assay (ELISA) for the highly sensitive detection of human C-reactive protein (CRP) in less than 30 min. It employs a one-step kinetics-based highly simplified and cost-effective sandwich ELISA procedure with minimal process steps. The procedure involves the formation of a sandwich immune complex on capture anti-human CRP antibody-bound Dynabeads in 15 min, followed by two magnet-assisted washings and one enzymatic reaction. The developed sandwich ELISA detects CRP in the dynamic range of 0.3 to 81 ng ml(-1) with a limit of detection of 0.4 ng ml(-1) and an analytical sensitivity of 0.7 ng ml(-1). It detects CRP spiked in diluted human whole blood and serum with high analytical precision, as confirmed by conventional sandwich ELISA. Moreover, the results of the developed ELISA for the determination of CRP in the ethylenediaminetetraacetic acid plasma samples of patients are in good agreement with those obtained by the conventional ELISA. The developed immunoassay has immense potential for the development of rapid and cost-effective in vitro diagnostic kits.

One step preparation and electrochemical analysis of IQS, a cell-cell communication signal in the nosocomial pathogen Pseudomonas aeruginosa.

Pseudomonas aeruginosa uses a hierarchical cell-cell communication system consisting of a number of regulatory elements to coordinate the expression of bacterial virulence genes. Sensitive detection of quorum sensing (QS) molecules has the potential for early identification of P. aeruginosa facilitating early medical intervention. A recently isolated cell-cell communication molecule, a thiazole termed IQS, can bypass the las QS system of P. aeruginosa under times of stress, activating a subset of QS-controlled genes. This compound offers a new target for pathogen detection and has been prepared in a one step protocol. A simple electrochemical strategy was employed for its sensitive detection using boron-doped diamond and glassy carbon electrodes by cyclic voltammetry and amperometry.

Self-assembly of a thin highly reduced graphene oxide film and its high electrocatalytic activity.

A thin highly reduced graphene oxide (rGO) film was self-assembled at the dimethyl formamide (DMF)-air interface through evaporation-induced water-assisted thin film formation at the pentane-DMF interface, followed by complete evaporation of pentane. The thin film was transferred onto various solid substrates for film characterization and electrochemical sensing. UV-visible spectrometry, scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemistry techniques were used to characterize the film. An rGO film showing 82.8% of the transmittance at 550 nm corresponds to a few layers of rGO nanosheets. The rGO nanosheets cross-stack with each other, lying approximately in the plane of the film. An rGO film collected on a glassy carbon (GC) electrode exhibited improved electrical conductivity compared to GC, with the electrode charge-transfer resistance (Rct) reduced from 31 Ω to 22 Ω. The as-formed rGO/GC electrode was mechanically very stable, exhibiting significantly enhanced electrocatalytic activity to H(2)O(2) and dopamine. Multiple layers of the rGO films on the GC electrode showed even stronger electrocatalytic activity to dopamine than that of the single rGO film layer. The controllable formation of a stable rGO film on various solid substrates has potential applications for nanoelectronics and sensors/biosensors.

CE with a boron-doped diamond electrode for trace detection of endocrine disruptors in water samples.

Off-line SPE and CE coupled with electrochemical detection have been used for the determination of bisphenol A (BPA), bisphenol F, 4-ethylphenol, and bisphenol A diglycidyl ether in bottled drinking water. The use of boron-doped diamond electrode as an electrochemical detector in amperometric mode that provides a favorable analytical performance for detecting these endocrine-disrupting compounds, such as lower noise levels, higher peak resolution with enhanced sensitivity, and improved resistance against electrode passivation. The oxidative electrochemical detection of the endocrine-disrupting compounds was accomplished by boron-doped diamond electrode poised at +1.4 V versus Ag/AgCl without electrode pretreatment. An off-line SPE procedure (Bond Elut® C18 SPE cartridge) was utilized to extract and preconcentrate the compounds prior to separation and detection. The minimum concentration detectable for all four compounds ranged from 0.01 to 0.06 µM, having S/N equal to three. After exposing the plastic bottle water container under sunlight for 7 days, the estimated concentration of BPA in the bottled drinking water was estimated to be 0.03 µM. This proposed approach has great potential for rapid and effective determination of BPA content present in water packaging of plastic bottles that have been exposed to sunlight for an extended period of time.

Zirconium-Coated ß-Cyclodextrin Nanomaterials for Biofilm Eradication.

Under alkaline treatment, zirconyl chloride (ZrOCl2.8H2O) became a zirconia gel and formed a stable complex with beta-cyclodextrin (ßCD). This complex was highly active in reactive oxygen species (ROS) formation via H2O2 decomposition. Its surface with numerous hydroxyl groups acts as an ionic sponge to capture the charged reaction intermediates, including superoxide (O2-•) and the hydroxyl radical (•OH). ROS, especially •OH radicals, are harmful to living microorganisms because of their kinetic instability, high oxidation potential, and chemical nonselectivity. Therefore, •OH radicals can engage in fast reactions with virtually any adjacent biomolecule. With H2O2, the complex with cationic and hydrophobic moieties interacted with the anionic bacterial membrane of two Gram-positive (Staphylococcus aureus and S. epidermidis) and two Gram-negative (Escherichia coli and Klebsiella pneumoniae) strains. The Zr-ßCD-H2O2 also eradicated more than 99% of the biofilm of these four pathogens. Considering the difficult acquisition of resistance to the oxidation of •OH, the results suggested that this ßCD-based nanomaterial might be a promising agent to target both drug-resistant pathogens with no cytotoxicity and exceptional antimicrobial activity.

Analysis and electroanalysis of perchlorate in water and food samples: a critical review.

Perchlorate, ClO4-, with diverse applications, has become one of the major contaminants in surface and groundwater sources. This highly soluble and stable anion poses a considerable threat to human health given that it contaminates drinking water, vegetables, milk, and other contaminated food products. ClO4- can impair the thyroid function; thus, drinking water with high levels of this anion is a severe problem worldwide. However, due to the high solubility, stability, and mobility of ClO4-, its remediation and monitoring remain a major challenge. Considering the various analytical methods, including electrochemistry, each method has advantages and disadvantages in terms of detection sensitivity, selectivity, analysis time, and cost. Also, sample preconcentration and clean-up must be performed for the analysis of more complex matrices such as food and biological samples to ensure a low detection limit and selectivity. Both ion chromatography (IC) and capillary electrophoresis (CE) coupled with electrochemical detection, in addition to liquid chromatography (LC)-mass spectrometry (MS), are expected to play key roles due to their lower detection limit with excellent sensitivities and selectivity. Herein, we also discuss the perspective on various electrode materials for the detection of ClO4- regarding whether ClO4- can be measured at the lowest levels with the highest selectivity.

Ultrasonic-assisted synthesis of lignin-capped Cu2O nanocomposite with antibiofilm properties.

Under ultrasonication, cuprous oxide (Cu2O) microparticles (<5 µm) were fragmented into nanoparticles (NPs, ranging from 10 to 30 nm in diameter), and interacted strongly with alkali lignin (Mw = 10 kDa) to form a nanocomposite. The ultrasonic wave generates strong binding interaction between lignin and Cu2O. The L-Cu nanocomposite exhibited synergistic effects with enhanced antibiofilm activities against E. coli, multidrug-resistant (MDR) E. coli, S. aureus (SA), methicillin-resistant SA, and P. aeruginosa (PA). The lignin-Cu2O (L-Cu) nanocomposite also imparted notable eradication of such bacterial biofilms. Experimental evidence unraveled the destruction of bacterial cell walls by L-Cu, which interacted strongly with the bacterial membrane. After exposure to L-Cu, the bacterial cells lost the integrated structural morphology. The estimated MIC for biofilm inhibition for the five tested pathogens was 1 mg/mL L-Cu (92 % lignin and 8 % Cu2ONPs, w/w %). The MIC for bacterial eradication was noticeably lower; 0.3 mg/mL (87 % lignin + 13 % Cu2ONPs, w/w %) for PA and SA, whereas this value was appreciably higher for MDR E. coli (0.56 mg/mL, 86 % lignin and 14 % Cu2O NPs). Such results highlighted the potential of L-Cu as an alternative to neutralize MDR pathogens.

Porous graphitized carbon monolith as an electrode material for probing direct bioelectrochemistry and selective detection of hydrogen peroxide.

For the first time, graphitized carbon particles with a high surface area have been prepared and evaluated as a new material for probing direct electrochemistry of hemoglobin (Hb). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging revealed that the carbon monolithic skeleton was constructed by a series of mesopores with irregular shapes and an average pore diameter of ~5.6 nm. With a surface area of 239.6 m(2)/g, carbon particles exhibited three major Raman peaks as commonly observed for carbon nanotubes and other carbon materials, i.e., the sp(3) and sp(2) carbon phases coexisted in the sample. A glassy carbon electrode modified with carbon monoliths and didodecyldimethylammonium bromide exhibited direct electron transfer between Hb molecules and the underlying electrode with a transfer rate constant of 6.87 s(-1). The enzyme electrode displayed a pair of quasi-reversible reduction-oxidation peaks at -0.128 and -0.180 V, reflecting the well-known feature of the heme [Fe(3+)/Fe(2+)] redox couple: a surface-controlled electrochemical process with one electron transfer. This reagentless biosensing approach was capable of detecting H(2)O(2), a simple molecule but plays an important role in analytical and biological chemistry, as low as 0.1 µM with linearity of 0.1-60 µM and a response time of <0.8 s, comparing favorably with other carbon based electrodes (5 s).

Rapid and simple preparation of a reagentless glucose electrochemical biosensor.

A rapid and simple procedure was developed for the preparation of a highly stable and leach-proof glucose oxidase (GOx)-bound glassy carbon electrode (GCE). Crosslinked GOx via glutaraldehyde was drop-cast on a KOH-pretreated GCE followed by drop-casting of 3-aminopropyltriethoxysilane (APTES) to form a stable bioactive layer. At -0.45 V, the biosensor exhibited a wide dynamic detection range of 0.5-48 mM for commercial glucose and 1.3-28.2 mM for Sugar-Chex blood glucose linearity standards. Several endogenous electroactive substances and drug metabolites commonly found in blood were tested and provoked no signal response. To our knowledge, the developed procedure is the most rapid method for preparing a glucose biosensor. The biosensor suffered no biofouling after 7 days of immersion in Sugar-Chex blood glucose. With excellent production reproducibility, GOx-bound electrodes stored dry at room temperature retained their initial activity after several weeks.

Important Roles and Potential Uses of Natural and Synthetic Antimicrobial Peptides (AMPs) in Oral Diseases: Cavity, Periodontal Disease, and Thrush.

Numerous epithelial cells and sometimes leukocytes release AMPs as their first line of defense. AMPs encompass cationic histatins, defensins, and cathelicidin to encounter oral pathogens with minimal resistance. However, their concentrations are significantly below the effective levels and AMPs are unstable under physiological conditions due to proteolysis, acid hydrolysis, and salt effects. In parallel to a search for more effective AMPs from natural sources, considerable efforts have focused on synthetic stable and low-cytotoxicy AMPs with significant activities against microorganisms. Using natural AMP templates, various attempts have been used to synthesize sAMPs with different charges, hydrophobicity, chain length, amino acid sequence, and amphipathicity. Thus far, sAMPs have been designed to target Streptococcus mutans and other common oral pathogens. Apart from sAMPs with antifungal activities against Candida albicans, future endeavors should focus on sAMPs with capabilities to promote remineralization and antibacterial adhesion. Delivery systems using nanomaterials and biomolecules are promising to stabilize, reduce cytotoxicity, and improve the antimicrobial activities of AMPs against oral pathogens. Nanostructured AMPs will soon become a viable alternative to antibiotics due to their antimicrobial mechanisms, broad-spectrum antimicrobial activity, low drug residue, and ease of synthesis and modification.

Cellulose Nanocrystals (CNC)-Based Functional Materials for Supercapacitor Applications.

The growth of industrialization and the population has increased the usage of fossil fuels, resulting in the emission of large amounts of CO2. This serious environmental issue can be abated by using sustainable and environmentally friendly materials with promising novel and superior performance as an alternative to petroleum-based plastics. Emerging nanomaterials derived from abundant natural resources have received considerable attention as candidates to replace petroleum-based synthetic polymers. As renewable materials from biomass, cellulose nanocrystals (CNCs) nanomaterials exhibit unique physicochemical properties, low cost, biocompatibility and biodegradability. Among a plethora of applications, CNCs have become proven nanomaterials for energy applications encompassing energy storage devices and supercapacitors. This review highlights the recent research contribution on novel CNC-conductive materials and CNCs-based nanocomposites, focusing on their synthesis, surface functionalization and potential applications as supercapacitors (SCs). The synthesis of CNCs encompasses various pretreatment steps including acid hydrolysis, mechanical exfoliation and enzymatic and combination processes from renewable carbon sources. For the widespread applications of CNCs, their derivatives such as carboxylated CNCs, aldehyde-CNCs, hydride-CNCs and sulfonated CNC-based materials are more pertinent. The potential applications of CNCs-conductive hybrid composites as SCs, critical technical issues and the future feasibility of this endeavor are highlighted. Discussion is also extended to the transformation of renewable and low-attractive CNCs to conductive nanocomposites using green approaches. This review also addresses the key scientific achievements and industrial uses of nanoscale materials and composites for energy conversion and storage applications.

Enhanced UV Protection, Heavy Metal Detection, and Antibacterial Properties of Biomass-Derived Carbon Dots Coated on Protective Fabrics.

Carbon dots (CDs) were simply prepared from charcoal by hydrothermal processing at 180 °C for 15 h without any chemicals. The as-prepared CDs with an average diameter of 5 ± 6 nm exhibited a predominant absorption peak at 290 nm, corresponding to the n to π* transition of the oxygen functional groups (C═O) and the free amine functional groups (-NH2). The resulting CDs were then incorporated into cotton and polyester by facile ultrasonication for 1 h. The obtained CD-coated fabrics were first evaluated for their UV-blocking capability and then for their antibacterial properties against two model pathogens: Gram-negative E. coli and Gram-positive S. aureus. Both cotton and polyester showed no UV protection at 280 or 380 nm; conversely, cotton or polyester decorated with CDs exhibited a UV blocking ratio of 82-98%. The CD-coated fabrics showed 100% antibacterial activities against E. coli and S. aureus, whereas the pristine fabrics showed no effect. The CDs/fabrics could adsorb Hg2+ and Fe3+, resulting in a drastic fluorescence quenching. As such, this distinct feature was exploited for the removal and detection of these two ions with the limits of detection of 55and 72 µM, respectively.

Cuprous Oxide Nanoparticles Decorated Fabric Materials with Anti-biofilm Properties.

Considering the global spread of bacterial infections, the development of anti-biofilm surfaces with high antimicrobial activities is highly desired. This work unraveled a simple, sonochemical method for coating Cu2O nanoparticles (NPs) on three different flexible substrates: polyester (PE), nylon 2 (N2), and polyethylene (PEL). The introduction of Cu2O NPs on these substrates enhanced their surface hydrophobicity, induced ROS generation, and completely inhibited the growth of sensitive (Escherichia coli and Staphyloccocus aureus) and drug-resistant (MDR E. coli and MRSA) planktonic and biofilm. The experimental results confirmed that Cu2O-PE exhibited complete biofilm mass reduction ability for all four strains, whereas Cu2O-N2 showed more than 99% biomass inhibition against both drug-resistant and sensitive pathogens in 6 h. Moreover, Cu2O-PEL also indicated a 99.95, 97.73, 98.00, and 99.20% biomass reduction of MRSA, MDR E. coli, E. coli, and S. aureus, respectively. All substrates were investigated for time-dependent inhibitions, and the associated biofilm mass and log reduction were evaluated. The mechanisms of Cu2O NP action against the mature biofilms include the generation of reactive oxygen species (ROS) as well as electrostatic interaction between Cu2O NPs and bacterial membranes. The current study could pave the way for the commercialization of sonochemically coated Cu2O NP flexible substrates for the prevention of microbial contamination in hospitals and industrial environments.

Sulfo-N-hydroxysuccinimide interferes with bicinchoninic acid protein assay.

This study revealed a major interference from sulfo-N-hydroxysuccinimide (sulfo-NHS) in the bicinchoninic acid (BCA) protein assay. Sulfo-NHS, a common reagent used in bioconjugation and analytical biochemistry, exhibited absorbance signals and absorbance peaks at 562 nm, comparable to bovine serum albumin (BSA). However, the combined absorbance of sulfo-NHS and BSA was not strictly additive. The sulfo-NHS interference was suggested to be caused by the reduction of Cu(2+) in the BCA Kit's reagent B (4% cupric sulfate) in a manner similar to that of the protein.