Response In pH Range Research Articles

Synergistic adsorption mechanism of novel combined collector in flotation separation of fayalite from magnetite: Experiments and MD simulations

As an iron-bearing silicate mineral, fayalite has similar surface properties to magnetite, which makes it challenging to efficiently separate fayalite from magnetite by flotation. In this study, magnetite and fayalite were separated using novel combined collector polyoxyethylene alkyl amine (PAE) and terpinol (AT) through reverse flotation. Combined with a variety of characterization analysis and molecular dynamics (MD) simulation, the synergistic adsorption mechanism of the combined collector on mineral surface was revealed from multiple perspectives. The optimum scheme and pH response range of the combined collector were determined by micro-flotation test. Compared with PAE alone, the difference value of flotation recovery between fayalite and magnetite using combined collector was increased by 10.16%, and the dosage was reduced by 20%. Additionally, an effectively adsorption of combined collector onto fayalite surface to improve its surface hydrophobicity. Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and MD simulations results showed synergistic adsorption was produced onto fayalite surface using combined collector mainly through non-polar interaction, hydrogen bond association and bridge adsorption. Furthermore, the spatial distribution and diffusion behavior of water molecules provide microscopic evidence for the enhancement of surface hydrophobicity of fayalite by combined collector.

A lysosome-targeting rhodamine fluorescent probe for Cu2+ detection and its applications in test kits and zebrafish imaging

Tracing copper ions levels in the environment and subcellular microenvironment is crucial due to the key role copper ions play in physiological and pathological processes. Herein, a novel naphthalimide-fused rhodamine probe Rh-Naph-Cu was prepared through modification with phenylhydrazine to produce a closed and non-fluorescent spirolactam. Based on the copper-induced spirolactam ring-opening and hydrolysis process, Rh-Naph-Cu can be employed as a fluorescence off–on probe for copper ions with high selectivity, high sensitivity (limit of detection: 33.0 nM), broad pH-response range (pH: 5.0–10.0), and color change visible with the naked eye. Rh-Nap-Cu could be made into test strips for the in-situ chromogenic detection of Cu2+. Significantly, Rh-Naph-Cu can be utilized for the detection of copper ions in living HeLa cells and zebrafish, and exhibits excellent lysosomal-targeting ability with high Pearson’s correlation coefficient (PCC) of 0.96.

Development of a 3D Hydrogel SERS Chip for Noninvasive, Real-Time pH and Glucose Monitoring in Sweat.

Traditional diagnostic methods, such as blood tests, are invasive and time-consuming, while sweat biomarkers offer a rapid physiological assessment. Surface-enhanced Raman spectroscopy (SERS) has garnered significant attention in sweat analysis because of its high sensitivity, label-free nature, and nondestructive properties. However, challenges related to substrate reproducibility and interference from the biological matrix persist with SERS. This study developed a novel ratio-based 3D hydrogel SERS chip, providing a noninvasive solution for real-time monitoring of pH and glucose levels in sweat. Encapsulating the probe molecule (4-MBN) in nanoscale gaps to form gold nanoflower-like nanotags with internal standards and integrating them into an agarose hydrogel to create a 3D flexible SERS substrate significantly enhances the reproducibility and stability of sweat analysis. Gap-Au nanopetals modified with probe molecules are uniformly dispersed throughout the porous hydrogel structure, facilitating the effective detection of the pH and glucose in sweat. The 3D hydrogel SERS chip demonstrates a strong linear relationship in pH and glucose detection, with a pH response range of 5.5-8.0 and a glucose detection range of 0.01-5 mM, with R2 values of 0.9973 and 0.9923, respectively. In actual sweat samples, the maximum error in pH detection accuracy is only 1.13%, with a lower glucose detection limit of 0.25 mM. This study suggests that the ratio-based 3D hydrogel SERS chip provides convenient, reliable, and rapid detection capabilities with substantial application potential for analyzing body fluid pH and glucose.

A dual-signals fluorometric and colorimetric peptide-based probe for Cu(II) and glyphosate detection and its application for bioimaging and water testing

A novel dual-signal fluorometric and colorimetric probe FMDH (5-FAM-Met-Asp-His-NH2), incorporating a tripeptide (Met-Asp-His-NH2) linked to 5-carboxyfluorescein (5-FAM), was firstly synthesised. FMDH demonstrated exceptional selectivity and sensitivity, rapid response, wide pH response range and robust anti-interference capabilities for monitoring Cu2+. This was achieved through a distinctive naked-eye colorimetric and fluorescent quenching behaviour. A good linearity within the range of 0–3 μM (R2 = 0.9914) was attained, and the limit of detection (LOD) for Cu2+ was 47.4 nM. Furthermore, the FMDH-Cu2+ ensemble responded to glyphosate with notable selectivity and sensitivity. A good linear correlation (R2 = 0.9926) was observed at the lower concentration range (2.4–7.8 μM) and achieving a detection limit as low as 29.9 nM. The response time of FMDH with Cu2+ and glyphosate were less than 20 s, and the pH range of 7–11 that was suitable for practical application under physiological pH conditions. MTT assays confirmed that FMDH offers good permeability and low toxicity, facilitating successful application in imaging analysis of Cu2+ and glyphosate in living cells and zebrafish. In addition, FMDH was employed in the detection of these analytes in real water samples. Cost-effective, highly sensitive and easily prepared FMDH-impregnated test strips were developed for the efficient visual detection of Cu2+ and glyphosate under 365 nm UV light. Increasing concentrations of Cu2+ and glyphosate resulted in notable colour changes under 365 nm UV light, enabling visual semi-quantitative analysis via a smartphone colour-analysis App.

In situ constructing of sulfur bedecked ZIF-67 with ultrahigh and selectivity UO22+ immobilization capability from seawater

Uranium, a strategically significant resource, is estimated to contain approximately 4.5 billion tons of unconventional uranium in seawater, which can be extracted as a sustainable fuel source for nuclear power plants. In this work, a sulfur bedecked ZIF-67 (SF@ZIF-67) uranium adsorbent were successfully fabricated by employing a facile hydrothermal sulfur functionalization approach. Sequential batch experiment showed that the SF@ZIF-67 specimen displayed a broader pH response range, exceptional UO22+ harvesting efficiency (Uinitial = ∼5–10 ppm, ∼90.68 %–93.79 %) and ultra-high uranium capture capacity (qmax = 769.23 mg/g). Remarkably, due to the strong affinity between sulfur functional groups and uranyl, the SF@ZIF-67 sample exhibited exceptional selectivity with a Kd value exceeding 104 mL/g even in the presence of diverse interfering ions. Moreover, the SF@ZIF-67 specimen showed a sustained uptake efficiency of 66.61 % with close 104 KdU value in a 3000-fold VO43− system. In natural uranium spiked-seawater (Uinitial = ∼10–1000 μg/L), SF@ZIF-67 can capture ∼21–2484.5 μg/g uranium after 24 h contact. Mechanism analysis confirmed that excellent uranyl fixation ability is attributed to the coordination of sulfur and oxygen terminals with uranyl, as well as the redox processes of S2− and U6+. This hydrothermal functionalization technique offers novel insights into the potential application of MOF materials for uranium extraction from seawater.

The interfacial electric field enhanced piezo-catalytic performance of Bi2S3/Ni/CN composites for peroxymonosulfate activation advanced oxidation processes (AOP) systems

The interfacial electric field of Bi2S3/Ni/CN composites has been found to enhance the piezo-catalytic performance in peroxymonosulfate activation for advanced oxidation processes (AOP) systems. This novel research field aims to strengthen AOP systems for pollutant control and degradation through the utilization of the piezo-catalysis. In this particular study, a hammer coral-like Bi2S3/Ni/CN composite with interfacial electric field was synthesized by incorporating bismuth sulfide into the Ni/CN matrix. The efficient separation of piezoelectric carriers and charge transfer between nickel and bismuth in the resulting Bi2S3/Ni/CN composite facilitate a synergistic effect in the activation of peroxymonosulfate (PMS). It has been observed that, when subjected to ultrasound, this composite can achieve a degradation rate exceeding 90% within a minute towards Rh B as a model dye. Notably, the degradation process is primarily driven by piezoelectric hole and mono-linear oxygen non-free radicals. Additionally, the interfacial electric field facilitates valence electron transfer and ultimately enhancing reaction efficiency. Experimental results further demonstrate that the removal efficiency of organic pollutants can surpass 98% within a pH range of 1–9 over a duration of 3 min, demonstrating wide pH response range and high catalytic activities.

New insights into sulfite activation by amorphous Fe1−xNixS for RhB removal: the synergistic effect of free radical and non-free radical pathway

Ni doping broadens the pH response range and accelerates the electron transfer rate, so that Fe1−xNixS/sulfite can remove RhB through the synergistic effect of free radical and non-free radical paths under different pH conditions.

A Highly fluorescent vinylene-linked covalent organic framework for chemical sensing of pH and NH3 gas with wide dynamic range

Herein, a vinylene-linked covalent organic framework (TMT-BPDA-COF) was prepared via the Aldol condensation of 2,4,6-trimethyl-1,3,5-triazine (TMT) and 4,4'-biphenyl dimethyl formaldehyde (BPDA). TMT-BPDA-COF displayed high crystallinity and thermal stability, and robust chemical stability in strong acid, strong base and common organic solvents. TMT-BPDA-COF nanosheets emitted strong yellow fluorescence with the quantum yield of 14.9% and showed fast reversible response toward pH with a wide range (pH 0.0 ∼ 14.0) based on the intramolecular charge transfer effect. Furthermore, portable fluorescent sensors were prepared by incorporated TMT-BPDA-COF nanosheets into agarose gel and cellulose acetate butyrate (CAB), respectively. TMT-BPDA-COF gel showed a wide pH response range over pH 0.0 ∼ 14.0 with a linear range of pH 4.0 ∼ 14.0. TMT-BPDA-COF CAB film exhibited high sensitivity for sensing of NH3 gas with a limit of detection of 1.6 ppb. TMT-BPDA-COF agarose gel and CAB film also exhibited good reversibility and reproducibility in response to pH and NH3 gas, respectively. We expect TMT-BPDA-COF-based sensors, which feature fast response, high sensitivity, wide response range, good reproducibility and reversibility, can apply to detect pH and NH3 gas in the field of environment and industry.

Protein proximity ligation probe with wide sensing range resolving dynamics of subcellular ph by super-resolution imaging

Subcellular pH plays a key role to modulate protein structures or specific active sites to impact diverse biological processes. The heterogeneity and high dynamics of intracellular pH require probes that can detect pH in the vicinity of the protein and have a wide pH response range. Here, we reported a protein proximity ligation fluorescent probe for super-resolution imaging of subcellular pH dynamics. Relying on SNAP-tag protein labeling technology, the pH-sensitive fluorophore BG-NDM based on photo-induced electron transfer mechanism was localized to the adjacent positions of the target protein in different subcellular organelles. The equilibrium between the non-fluorescent aggregate and the fluorogenic monomer enabled BG-NDM to have the ability of wash-free super-resolution imaging in live cells. And the wide pH response ranges from pH 6 to pH 12 made the probe have the ability of recognizing pH dynamics. The pH changes around functional proteins during mitophagy, cellular alkalosis and acidosis were revealed. Through long-term super-resolution imaging, we could further record the pH dynamics around mitochondrial proteins COX8A during mitochondrial contacts, fusion and fission at the resolution of a single mitochondria.

One‐step Fabrication of Nitrogen‐Doped Carbon Dots‐Based Fluorescent Sensors with Red Emission for Efficient Detection of pH

AbstractCarbon dots have been widely noticed due to their excellent optical properties, such as good photostability and a wide excitation wavelength range. However, the emission peaks of most known carbon dots (CDs) are in the blue region, which hinders their extensive applications in long‐wavelength emission. In this study, red‐emitting carbon dots (RCDs) that are pH‐responsive are synthesized using citric acid and urea as precursors, and their fluorescence intensity increased gradually with increasing solution pH from 1 to 12. A new mechanism based on H aggregation and Fermi energy level transfer is proposed to explain the pH‐responsive emission of RCDs. In contrast to the narrow response range of most pH‐sensitive CDs reported so far, the pH‐responsive range of RCDs is large, especially in the alkaline range, and their pronounced red light emission is well visualized. The prepared carbon dots have the advantages of non‐toxicity, low cost, and a wide pH response range. In addition, “rose” test paper and carbon dot PVA composite film, RCDs‐PVA film, are made to demonstrate the visualization of carbon dots in pH detection. The “rose” test paper and carbon dot PVA still have good fluorescence intensity. The prepared carbon dots have good application prospects for pH detection.

Rapid and visual evaluation the internal corruption of meat tissue by a designed near-infrared fluorescence probe with a broad pH response range

Rapid and visual evaluation the internal corruption of meat tissue is closely related to public health. The pH change caused by glycolysis and amino acid decomposition is an important indicator of meat freshness. Herein, we designed a pH-responsive NIR fluorescent probe (Probe-OH) based on protonation/deprotonation for monitoring the internal corruption of meat tissue. Probe-OH was synthesized by a stable hemicyanine skeleton with phenolic hydroxyl group, which exhibited excellent performances such as high selectivity, high sensitivity, fast response time (60 s), a broad pH-responsive range of 4.0–10.0, and superior spatio-temporal sampling ability. In addition, we conducted a paper chip platform to measure pH value in different meat samples (pork and chicken), which is convenient to evaluate pH value of meat by observing the color changes of paper strips. Furthermore, in combination with the NIR advantages of fluorescence imaging, Probe-OH was successfully applied to assess the freshness of pork and chicken breasts, and the structural changes of muscle tissue can be clearly observed under confocal microscope. The results of Z-axis scanning showed that Probe-OH could penetrate into the interior to monitor the internal corruption of meat tissue, the fluorescence intensity changes with scanning height in the meat tissue section, and reaches its maximum at 50 μm. To the best of our knowledge, there have been no reports of fluorescence probe being used to image the inside of meat tissue section so far. It is expected that we can provide a new rapid, sensitive, near-infrared fluorescence method for assessment of the freshness in the internal organization of meat.

An antibacterial and intelligent cellulose-based label self-assembled via electrovalent bonds for a multi-range sensing of food freshness

Intelligent labels provide customers with food freshness information. However, the existing label response is limited and can only detect a single kind of food. Here, an intelligent cellulose-based label with highly antibacterial activity for a multi-range sensing freshness was developed to overcome the limitation. Cellulose fibers were modified using oxalic acid to graft -COO− followed by binding chitosan quaternary ammonium salt (CQAS), the remaining charges of which attached methylene red and bromothymol blue to form response fibers and to further self-assemble into the intelligent label. CQAS electrostatically gathered the dispersed fibers, resulting in an increase in TS and EB of 282 % and 16.2 %, respectively. After that, the rest positive charges fixed the anionic dyes to broaden pH response range of 3–9 effectively. More significantly, the intelligent label exhibited highly antimicrobial activity, killing 100 % of staphylococcus aureus. The rapid acid-base response revealed the potential for practical application in which the label color from green to orange represented the milk or spinach from fresh to close to spoiled, and from green to yellow, and to light green indicated the pork fresh, acceptable, and close to spoiled. This study paves a way for the preparation of intelligent labels in large-scale and promote the commercial application to improve food safety.

A highly effective "naked eye" colorimetric and fluorimetric curcumin-based fluorescent sensor for specific and sensitive detection of H2O2in vivo and in vitro.

Hydrogen peroxide (H2O2) is involved in many important tasks in normal cell metabolism and signaling. However, abnormal levels of H2O2 are associated with the occurrence of several diseases. Therefore, it is important to develop a new method for the detection of H2O2in vivo and in vitro. A turn-off sensor, 2,2-difluoro-4,6-bis(3-methoxy-4-((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)styryl)-2H-1,3,2-dioxaborine (DFCB), based on curcumin was developed for the detection of H2O2. The DFCB, an orange-emitting sensor, was constructed by employing 2,2-difluoro-4,6-bis(4-hydroxy-3-methoxystyryl)-2H-1,3,2-dioxaborine (DFC) as the main carrier, and 2-(4-bromomethylphenyl)-4,4,5,5-tetramethyl-1,3,2-doxaborolane as the recognition site. The recognition group on the DFCB sensor could be completely cleaved by H2O2 to generate the intermediate DFC, which would lead to a colorimetric change from bright orange to light blue accompanying by a significantly quenched fluorescence, which could be seen by the naked eye. This sensor exhibited a highly specific fluorescence response to H2O2, in preference to other relevant species, with an excellent anti-interference performance. The sensor DFCB also possessed some advantages including a wide pH response range (6-11), a broad linear range (0-300 μM), and a low detection limit (1.31 μM). The sensing mechanism of the DFCB sensor for H2O2 was verified by HRMS analysis, 1H-NMR titration and DFT calculations. In addition, the use of the DFCB sensor was compatible with the fluorescence imaging of H2O2 in living cells and zebrafish.

Composite film with adjustable number of layers for slow release of humic acid and soil remediation

In this study, to improve the soil amendment performance of film materials, composite films with the adjustable number of layers and controlled slow-release time were prepared using sodium alginate (SA), chitosan (CS) and activated charcoal (AC) as raw materials. The prepared multilayer films exhibited a wide pH response range and excellent slow-release time. The cumulative release of humic acid (HA) increased from 19.87 ± 0.98% to 66.72 ± 1.06% with increasing the pH from 4.0 to 10.0 after 700 h of slow-release. In addition, after 50 d of remediation in red soil, plantation soil, and saline soil, the NH4+-N, Olsen-P, Olsen-K, and organic matter contents in the three soils were increased by 2.91–28.62 mg/kg, 46.97–70.43 mg/kg, 55.89–77.01 mg/kg, and 12.47–22.52 g/kg, respectively, and were able to provide sustained crop growth promotion effect. This study demonstrates the promising application of multilayer film in soil remediation and agricultural production.

The pH Robustness of Bacterial Sensing.

ABSTRACTBacteria have evolved many different signal transduction systems to sense and respond to changing environmental conditions. Signal integration is mainly achieved by signal recognition at extracytosolic ligand-binding domains (LBDs) of receptors. Hundreds of different LBDs have been reported, and our understanding of their sensing properties is growing. Receptors must function over a range of environmental pH values, but there is little information available on the robustness of sensing as a function of pH. Here, we have used isothermal titration calorimetry to determine the pH dependence of ligand recognition by nine LBDs that cover all major LBD superfamilies, of periplasmic solute-binding proteins, and cytosolic LBDs. We show that periplasmic LBDs recognize ligands over a very broad pH range, frequently stretching over eight pH units. This wide pH range contrasts with a much narrower pH response range of the cytosolic LBDs analyzed. Many LBDs must be dimeric to bind ligands, and analytical ultracentrifugation studies showed that the LBD of the Tar chemoreceptor forms dimers over the entire pH range tested. The pH dependences of Pseudomonas aeruginosa motility and chemotaxis were bell-shaped and centered at pH 7.0. Evidence for pH robustness of signaling in vivo was obtained by Förster Resonance Energy Transfer (FRET) measurements of the chemotaxis pathway responses in Escherichia coli. Bacteria have evolved several strategies to cope with extreme pH, such as periplasmic chaperones for protein refolding. The intrinsic pH resistance of periplasmic LBDs appears to be another strategy that permits bacteria to survive under adverse conditions.

CuCo and sulfur doped carbon nitride composite as an effective Fenton-like catalyst in a wide pH range.

The heterogeneous Fenton-like reaction, as an advanced oxidation process, is widely recognized attributed to its recyclability, wide pH response range, easy solid-liquid separation, and non-production of iron sludge. Recently, the bimetallic catalysts have attracted intense attention due to their high catalytic performance and excellent stability over a wide pH range. In this article, CuCo/SCN bimetallic catalyst was prepared by pyrolysis method with sulfur doped carbon nitride (SCN) as the carrier. Under the conditions of pH = 7, catalyst dosage of 0.8 g/L, and concentration of H2O2 of 15 mM, 20 mg/L of methyl orange (MO) can be completely removed within 1 h. With the synergistic action between bimetals and sulfur doped carbon nitride, the CuCO/SCN involved Fenton-like system exhibited excellent catalytic degradation efficiency and strong stability for MO in neutral and weak alkaline conditions. The EPR characterization proved that OH and O2 − were the main active components. Furthermore, CuCo/SCN involved Fenton-like system has good adaptability. Bimetallic CuCo/SCN catalyst has great application potential in the degradation of environmental pollutants.

Molecular engineering to construct specific cancer cell lysosome targeting photosensitizer by adjusting the proton binding ability

Minimizing the concomitant damage to healthy tissues is the key factor to guarantee precise and efficient photodynamic therapy (PDT). Herein, a specifically cancer cell lysosome targeted pre-photosensitizer with the suitable pH-response range (pH < 5.0) has been rationally designed by simple molecular engineering and successfully applied for switch-on PDT, which is further confirmed by the single crystal structure, pH test, cell uptake, and in vivo treatments. Fluorescence imaging on mouse model evidences that it is “off” in normal tissue and “on” in tumor region. This lysosome-targeting activated pre-photosensitizer provides new opportunities in the rational design of tumor specifically responsive photosensitizer.

A near-infrared ratiometric fluorescent probe with large stokes shift for rapid detection of ClO− in living cells

Both of lipid droplets (LDs) and hypochlorous acid/hypochlorite (HClO/ClO−) play important roles in regulating cell metabolism and maintaining normal operation of life activities. Here, we report the synthesis of probe T, which is a typical compound with AIE properties. The probe T can not only detect ClO− by proportional fluorescence, but also specifically target LDs. T displayed an excellent spectral performance with a long emission wavelength (715 nm), large stokes shift (211 nm), wide pH response range. When it encountered ClO−, the fluorescence color changed from red to blue with a large fluorescence signal shift (from 715 nm to 430 nm) and good sensitivity (detection limit: 0.102 μM). More interestingly, we successfully advanced the response speed of T to ClO− by loading the AIE probe with protein. Additionally, cell imaging experiments demonstrated that T was perfectly utilized to visualize exogenous/endogenous ClO− in cells and possessed an excellent LDs-targeting ability.

Lysosome-Targeted Biosensor for the Super-Resolution Imaging of Lysosome-Mitochondrion Interaction.

Background: The interaction between lysosomes and mitochondria includes not only mitophagy but also mitochondrion–lysosome contact (MLC) that enables the two organelles to exchange materials and information. In our study, we synthesised a biosensor with fluorescence characteristics that can image lysosomes for structured illumination microscopy and, in turn, examined morphological changes in mitochondria and the phenomenon of MLC under pathological conditions. Methods: After designing and synthesising the biosensor, dubbed CNN, we performed an assay with a Cell Counting Kit-8 to detect CNN’s toxicity in relation to H9C2 cardiomyocytes. We next analysed the co-localisation of CNN and the commercial lysosomal probe LTG in cells, qualitatively analysed the imaging characteristics of CNN in different cells (i.e. H9C2, HeLa and HepG2 cells) via structured illumination microscopy and observed how CNN entered cells at different temperatures and levels of endocytosis. Last, we treated the H9C2 cells with mannitol or glucose to observe the morphological changes of mitochondria and their positions relative to lysosomes. Results: After we endocytosed CNN, a lysosome-targeted biosensor with a wide, stable pH response range, into cells in an energy-dependent manner. SIM also revealed that conditions in high glucose induced stress in lysosomes and changed the morphology of mitochondria from elongated strips to round spheres. Conclusion: CNN is a new tool for tracking lysosomes in living cells, both physiologically and pathologically, and showcases new options for the design of similar biosensors.

Rational design of dual-functional peptide-based chemosensor for sequential detection of Ag+ (AgNPs) and S2− ions by fluorescent and colorimetric changes and its application in live cells, real water samples and test strips

A novel bifunctional chemosensor L with excellent fluorescent group FITC labelled at tetrapeptide (CysProGlyHis-NH2) was designed and developed. L exhibited fluorescent quenching response and unique visual color change for Ag+ and AgNPs in aqueous solution. The stoichiometry between L and Ag+ was confirmed to be 1:1 based on fluorescent titration, Job's plot, ESI-HRMS and theoretical calculation studies. In particular, the limit of detection (LOD) of L for the detection of Ag+ and AgNPs were calculated as 3.35 nM and 4.57 nM, respectively. In addition, the L-Ag complex as a new relay chemosensor could be highly selective detection of S2−via obvious color and fluorescence changes, which could be monitored by the naked eye. The LOD for S2− was as low as to be 28.17 nM with high sensitivity. Furthermore, L indicated a rapid response (within 50 s), exciting circularity (more than 10 times) and wide pH response range (6 ∼ 12). Moreover, in view of excellent stability, low cytotoxicity and biocompatibility, we further successfully applied L for Ag+, AgNPs and S2− detection and imaging in living cells, real water samples and test strips.