Electrogenerated chemiluminescence ethanol biosensor based on alcohol dehydrogenase functionalized Ru(bpy)3 doped silica nanoparticles

An ethanol biosensor, based on the electrogenerated chemiluminescence of Ru(bpy)₃²⁺-doped silica nanoparticles (RuSiNPs), was investigated in this study. The biosensor was a modified glassy carbon electrode, where alcohol dehydrogenase was crosslinked to RuSiNPs, and then immobilized on the electrode surface using chitosan. The results indicated that the biosensor exhibited excellent performance during ethanol determination with a wide linear range (10⁻⁷ to 10⁻² M), low detection limit (5.0 × 10⁻⁸ M) and good stability.     

An amperometric biosensor fabricated from electro-co-deposition of sodium alginate and horseradish peroxidase

A convenient and effective strategy for fabrication of hydrogen peroxide biosensor based on sodium alginate (SA) and polyvinyl butyral (PVB) as matrices was reported in this paper. The horseradish peroxidase (HRP) and SA were electro-co-deposited onto the surface of gold electrode, and the HRP–SA/Au electrode was further coated with PVB. The interaction between HRP and SA was characterized by UV–vis absorption spectroscopy, and the fabricating process of biosensor was characterized by electrochemical impedance spectroscopy (EIS). The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. Experimental conditions were investigated which influence the performance of the biosensor, such as pH, and applied potential. The biosensor showed a linear response to H₂O₂ over a concentration range from 7.0 × 10⁻⁶ to 4.1 × 10⁻³ M with a detection limit of 1.8 × 10⁻⁶ M based on a signal-to-noise ratio of 3 under optimum conditions. The value of HRP in the composite was evaluated to be 1.38 mM. The biosensor obtained from this study possesses high sensitivity, good reproducibility, and long-term stability.     

A nano-Ni based ultrasensitive nonenzymatic electrochemical sensor for glucose: Enhancing sensitivity through a nanowire array strategy

Highly ordered Ni nanowire arrays (NiNWAs) were synthesized for the first time using a template-directed electropolymerization strategy with a nanopore polycarbonate (PC) membrane template, and their morphological characterization were examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). A NiNWAs based electrode shows very high electrochemical activity for electrocatalytic oxidation of glucose in alkaline medium, which has been utilized as the basis of the fabrication of a nonenzymatic biosensor for electrochemical detection of glucose. The biosensor can be applied to the quantification of glucose with a linear range covering from 5.0 × 10⁻⁷ to 7.0 × 10⁻³ M, a high sensitivity of 1043 μA mM⁻¹ cm⁻², and a low detection limit of 1 × 10⁻⁷ M. The experiment results also showed that the sensor exhibits good reproducibility and long-term stability, as well as high selectivity with no interference from other oxidable species.     

Xanthine oxidase/laponite nanoparticles immobilized on glassy carbon electrode: Direct electron transfer and multielectrocatalysis

In this work, colloidal laponite nanoparticles were further expanded into the design of the third-generation biosensor. Direct electrochemistry of the complex molybdoenzyme xanthine oxidase (XnOx) immobilized on glassy carbon electrode (GCE) by laponite nanoparticles was investigated for the first time. XnOx/laponite thin film modified electrode showed only one pair of well defined and reversible cyclic voltammetric peaks attributed to XnOx–FAD cofactor at about −0.370 V vs. SCE (pH 5). The formal potential of XnOx–FAD/FADH₂ couple varied linearly with the increase of pH in the range of 4.0–8.0 with a slope of −54.3 mV pH⁻¹, which indicated that two-proton transfer was accompanied with two-electron transfer in the electrochemical reaction. More interestingly, the immobilized XnOx retained its biological activity well and displayed an excellent electrocatalytic performance to both the oxidation of xanthine and the reduction of nitrate. The electrocatalytic response showed a linear dependence on the xanthine concentration ranging from 3.9 × 10⁻⁸ to 2.1 × 10⁻⁵ M with a detection limit of 1.0 × 10⁻⁸ M based on S/N = 3.     

Hybridization biosensor using 2-nitroacridone as electrochemical indicator for detection of short DNA species of Chronic Myelogenous Leukemia

A new acridone derivative 2-nitroacridone (NAD) was synthesized in this paper, and it was found that NAD had excellent electrochemical activity on the glassy carbon electrode (GCE) with a couple reversible redox peaks at 0.051 V and 0.103 V, respectively. Voltammetry was used to investigate the electrochemical behavior of NAD and the interaction between NAD and salmon sperm DNA. In pH 4.0 phosphate buffer solution, the binding ratio between NAD and salmon sperm DNA was calculated to be 2:1 and the binding constant was 3.19 × 10⁵ L/mol. A Chronic Myelogenous Leukemia (CML, Type b₃a₂) DNA biosensor was developed by immobilizing covalently single-stranded CML DNA fragments to a modified GCE. The surface hybridization of the immobilized single-stranded CML DNA fragment with its complementary DNA fragment was evidenced by electrochemical methods using NAD as a novel electrochemical indicator, with a detection limit of 6.7 × 10⁻⁹ M and a linear response range of 1.8 × 10⁻⁸ M to 9.1 × 10⁻⁸ M for CML DNA. Selective determination of complementary ssDNA was achieved using differential pulse voltammetry (DPV).     

Glucose biosensor based on immobilization of glucose oxidase in poly(o-aminophenol) film on polypyrrole-Pt nanocomposite modified glassy carbon electrode

Novel Pt nanoclusters embedded polypyrrole nanowires (PPy-Pt) composite was electrosynthesized on a glassy carbon electrode, denoted as PPy-Pt/GCE. A glucose biosensor was further fabricated based on immobilization of glucose oxidase (GOD) in an electropolymerized non-conducting poly(o-aminophenol) (POAP) film that was deposited on the PPy-Pt/GCE. The morphologies of the PPy nanowires and PPy-Pt nanocomposite were characterized by field emission scanning electron microscope (FE-SEM). Effect of experimental conditions involving the cycle numbers for POAP deposition and Pt nanoclusters deposition, applied potential used in glucose determination, temperature and pH value of the detection solution were investigated for optimization. The biosensor exhibited an excellent current response to glucose over a wide linear range from 1.5 × 10⁻⁶ to 1.3 × 10⁻² M (r = 0.9982) with a detection limit of 4.5 × 10⁻⁷ M (s/n = 3). Based on the combination of permselectivity of the POAP and the PPy films, the sensor had good anti-interference ability to ascorbic acid (AA), uric acid (UA) and acetaminophen. The apparent Michaelis–Menten constant (K_m) and the maximum current density (I_m) were estimated to be 23.9 mM and 378 μA/cm², respectively. In addition, the biosensor had also good sensitivity, stability and reproducibility.     

Zinc oxide/redox mediator composite films-based sensor for electrochemical detection of important biomolecules

Electrochemical oxidation of serotonin (SN) onto zinc oxide (ZnO)-coated glassy carbon electrode (GCE) results in the generation of redox mediators (RMs) that are strongly adsorbed on electrode surface. The electrochemical properties of zinc oxide-electrogenerated redox mediator (ZnO/RM) (inorganic/organic) hybrid film-coated electrode has been studied using cyclic voltammetry (CV). The scanning electron microscope (SEM), atomic force microscope (AFM), and electrochemical techniques proved the immobilization of ZnO/RM core/shell microparticles on the electrode surface. The GCE modified with ZnO/RM hybrid film showed two reversible redox peaks in acidic solution, and the redox peaks were found to be pH dependent with slopes of −62 and −60 mV/pH, which are very close to the Nernst behavior. The GCE/ZnO/RM-modified electrode exhibited excellent electrocatalytic activity toward the oxidations of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in 0.1 M phosphate buffer solution (PBS, pH 7.0). Indeed, ZnO/RM-coated GCE separated the anodic oxidation waves of DA, AA, and UA with well-defined peak separations in their mixture solution. Consequently, the GCE/ZnO/RMs were used for simultaneous detection of DA, AA, and UA in their mixture solution. Using CV, calibration curves for DA, AA, and UA were obtained over the range of 6.0 × 10⁻⁶ to 9.6 × 10⁻⁴ M, 1.5 × 10⁻⁵ to 2.4 × 10⁻⁴ M, and 5.0 × 10⁻⁵ to 8 × 10⁻⁴ M with correlation coefficients of 0.992, 0.991, and 0.989, respectively. Moreover, ZnO/RM-modified GCE had good stability and antifouling properties.     

Pine nut peroxidase immobilized on chitosan crosslinked with citrate and ionic liquid used in the construction of a biosensor

A biosensor based on the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI·Tf₂N) and a novel source of peroxidase (tissue from the pine nuts of Araucaria angustifolia) was constructed. This enzyme was immobilized on chitosan crosslinked with citrate and the biosensor used for the determination of rosmarinic acid by square-wave voltammetry. The peroxidase in the presence of hydrogen peroxide catalyzes the oxidation of rosmarinic acid to quinone and the electrochemical reduction of the product was obtained at a potential of +0.15 V vs. Ag/AgCl. Different analytical parameters influencing the biosensor response, that is, peroxidase units, pH, hydrogen peroxide concentration and parameters for the square-wave voltammetry (frequency, pulse amplitude and scan increment), were investigated. The best performance was observed for the biosensor under the following conditions: 1000 units mL⁻¹ peroxidase, pH 7.0 and 8.3 × 10⁻⁴ mol L⁻¹ hydrogen peroxide with a frequency of 30 Hz, pulse amplitude of 100 mV and scan increment of 5.0 mV. The biosensor gave a linear response to rosmarinic acid over the concentration range of 9.07 × 10⁻⁷ to 4.46 × 10⁻⁶ mol L⁻¹ with a detection limit of 7.25 × 10⁻⁸ mol L⁻¹. The recovery of rosmarinic acid in plant extracts ranged from 97.0% to 109.6% and the determination of this substance in these samples using the biosensor compared favorably with that using the capillary electrophoresis method.     

Glucose biosensor based on the room-temperature phosphorescence of TiO2/SiO2 nanocomposite

The direct immobilization of glucose oxidase (GOD) on TiO₂/SiO₂ nanocomposite and its application as glucose biosensor were investigated. The room-temperature phosphorescence of TiO₂/SiO₂ nanocomposite can be quenched by hydrogen peroxide (H₂O₂). The detection of glucose may be accomplished by monitoring the formation of hydrogen peroxide which generated in the oxidation process of glucose with the catalysis of GOD. To our surprise, by using a 96-hole polyporous plate accessory of fluorescence spectrophotometer, the biosensor exhibits excellent linear response to glucose concentrations ranging from 1.0 × 10⁻⁹ to 1.0 × 10⁻² M with a detection limit of 1.2 × 10⁻¹⁰ M. The TiO₂/SiO₂ nanocomposite can be used as both supporting material and signal transducer. The phosphorescence intensity and color of the biosensor change obviously and even could be observed with naked eyes by continuous addition of glucose. Based on the room-temperature phosphorescence of TiO₂/SiO₂ nanocomposite, a new method of solid substrate-room-temperature phosphorimetry (SS-RTP) for glucose determination is proposed. A glucose biosensor was fabricated with wide determination concentration range, low detection limit, high sensitivity, and fast response time. And the biosensor has been successfully applied to the determination of glucose in human blood serum. The coacervation of GOD enzyme and its interaction with TiO₂/SiO₂ nanocomposite enlarge the surface area and enhance the chemical stability of GOD. The nice biocompatibility, large surface area, good chemical stability and nontoxicity of the TiO₂/SiO₂ nanocomposite have made this material suitable for functioning as biosensor.     

Silver electrodeposition catalyzed by colloidal gold on carbon paste electrode: application to biotin–streptavidin interaction monitoring

A new electrochemical method to monitor biotin–streptavidin interaction on carbon paste electrode, based on silver electrodeposition catalyzed by colloidal gold, was investigated. Silver reduction potential changed when colloidal gold was attached to an electrode surface through the biotin–streptavidin interaction. Thus, the direct reduction of silver ions on the electrode surface could be avoided and therefore, they were only reduced to metallic silver on the colloidal gold particle surface, forming a shell around these particles. When an anodic scan was performed, this shell of silver was oxidized and an oxidation process at +0.08 V was recorded in NH₃ 1.0 M. Biotinylated albumin was adsorbed on the pretreated electrode surface. This modified electrode was immersed in colloidal gold-streptavidin labeled solutions. The carbon paste electrode was then activated in adequate medium (NaOH 0.1 M and H₂SO₄ 0.1 M) to remove proteins from the electrode surface while colloidal gold particles remained adsorbed on it. Then, a silver electrodeposition at −0.18 V for 2 min and anodic stripping voltammetry were carried out in NH₃ 1.0 M containing 2.0×10⁻⁵ M of silver lactate. An electrode surface preparation was carried out to obtain a good reproducibility of the analytical signal (5.3%), using a new electrode for each experiment. In addition, a sequential competitive assay was carried out to determine streptavidin. A linear relationship between peak current and logarithm of streptavidin concentration from 2.25×10⁻¹⁵ to 2.24×10⁻¹² M and a limit of detection of 2.0×10⁻¹⁵ M were obtained.     

Laccase-catalyzed oxidation of phenolic compounds in organic media

Rhus vernificera laccase-catalyzed oxidation of phenolic compounds, i.e., (+)-catechin, (−)-epicatechin and catechol, was carried out in selected organic solvents to search for the favorable reaction medium. The investigation on reaction parameters showed that optimal laccase activity was obtained in hexane at 30 °C, pH 7.75 for the oxidation of (+)-catechin as well as for (−)-epicatechin, and in toluene at 35 °C, pH 7.25 for the oxidation of catechol. E_a and Q₁₀ values of the biocatalysis in the reaction media of the larger log p solvents like isooctane and hexane were relatively higher than those in the reaction media of lower log p solvents like toluene and dichloromethane. Maximum laccase activity in the organic media was found with 6.5% of buffer as co-solvent. A wider range of 0–28 μg protein/ml in hexane than that of 0–16.7 μg protein/ml in aqueous medium was observed for the linear increasing conversion of (+)-catechin. The kinetic studies revealed that in the presence of isooctane, hexane, toluene and dichloromethane, the K_m values were 0.77, 0.97, 0.53 and 2.9 mmol/L for the substrate of (+)-catechin; 0.43, 0.34, 0.14 and 3.4 mmol/L for (−)-epicatechin; 2.9, 1.8, 0.61 and 1.1 mmol/L for catechol, respectively, while the corresponding V_max values were 2.1 × 10⁻², 2.3 × 10⁻², 0.65 × 10⁻² and 0.71 × 10⁻² δA/μg protein min); 1.8 × 10⁻², 0.88 × 10⁻², 0.19 × 10⁻² and 1.0 × 10⁻² δA/μg protein min); 0.48 × 10⁻², 0.59 × 10⁻², 0.67 × 10⁻² and 0.54 × 10⁻² δA/μg protein min), respectively. FT-IR indicated the formation of probable dimer from (+)-catechin in organic solvent. These results suggest that this laccase has higher catalytic oxidation capacity of phenolic compounds in suitable organic media and favorite oligomers could be obtained.     

Development of an amperometric assay for phosphate ions in urine based on a chemically modified screen-printed carbon electrode

An amperometric assay for the determination of inorganic phosphate (Pi) in urine has been developed without the need for sample preparation. A screen-printed carbon electrode modified with the electrocatalyst cobalt phthalocyanine (CoPC–SPCE) and covered with a cellulose acetate membrane (CAM) serves as the sensor. The sensor detects hydrogen peroxide (H₂O₂), which is produced as a result of the oxidative decarboxylation of pyruvate, catalyzed by pyruvate oxidase (PyOd), in the presence of Pi, oxygen, and cofactors. Following optimization of solution conditions, and in the presence of a urine sample, a linear range was found to exist between the rate of current increase and phosphate concentration over the range of 2.27 × 10⁻⁵ to 1.81 × 10⁻⁴ M, and the limit of detection was found to be 4.27 × 10⁻⁶ M. The assay was applied to the determination of phosphate ions in the urine of a normal subject, and the mean concentration in unspiked urine was found to be 3.40 × 10⁻⁵ M with a coefficient of variation of 8.0% (n = 5). The mean recovery of phosphate added to urine samples was 98.7% with a coefficient of variation of 5.5% (n = 3). To the authors’ knowledge, this is the first report of an amperometric assay for Pi that incorporates a CoPC–SPCE as the sensing device.     

Direct oxidation of boronates by peroxynitrite: Mechanism and implications in fluorescence imaging of peroxynitrite

In this study, we show that boronates, a class of synthetic organic compounds, react rapidly and stoichiometrically with peroxynitrite (ONOO⁻) to form stable hydroxy derivatives as major products. Using a stopped-flow kinetic technique, we measured the second-order rate constants for the reaction with ONOO⁻, hypochlorous acid (HOCl), and hydrogen peroxide (H₂O₂) and found that ONOO⁻ reacts with 4-acetylphenylboronic acid nearly a million times (k = 1.6 × 10⁶ M^− 1 s^− 1) faster than does H₂O₂ (k = 2.2 M^− 1 s^− 1) and over 200 times faster than does HOCl (k = 6.2 × 10³ M^− 1 s^− 1). Nitric oxide and superoxide together, but not alone, oxidized boronates to the same phenolic products. Similar reaction profiles were obtained with other boronates. Results from this study may be helpful in developing a novel class of fluorescent probes for the detection and imaging of ONOO⁻ formed in cellular and cell-free systems.     

Graphitized macroporous carbon microarray with hierarchical mesopores as host for the fabrication of electrochemical biosensor

A novel graphitized ordered macroporous carbon (GMC, pore size 380 nm) with hierarchical mesopores (2–30 nm) and high graphitization degree was prepared by nickel-catalyzed graphitization of polystyrene arrays. The obtained GMC possessed high specific surface area, large pore volume, and good electrical conductivity, which was explored for the enzyme entrapment and biosensor fabrication by a facile method. With advantages of novel nanostructure and good electrical conductivity, direct electrochemistry of hemoglobin (a model protein) was observed on the GMC-based biocomposite with a formal potential of −0.36 V (vs. Ag/AgCl) and an apparent heterogeneous electron transfer rate constant (k_s) of 1.2 s⁻¹ in pH 7.0 buffer. Comparative studies revealed that GMC offered significant advantages over carbon nanotubes (CNTs) in facilitating direct electron transfer of entrapped Hb. The fabricated biosensor exhibited good sensitivity (101.6 mA cm⁻² M⁻¹) and reproducibility, wide linear range (1–267 μM), low detection limit (0.1 μM), and good long-term stability for H₂O₂ detection. GMC proved to be a promising matrix for enzyme entrapment and biosensor fabrication, and may find wide potential applications in biomedical detection and environmental analyses.     

Selective electrochemical sensor for folic acid at physiological pH using ultrathin electropolymerized film of functionalized thiadiazole modified glassy carbon electrode

This paper demonstrated the selective determination of folic acid (FA) in the presence of important physiological interferents, ascorbic acid (AA) and uric acid (UA) at physiological pH using electropolymerized film of 5-amino-2-mercapto-1,3,4-thiadiazole (p-AMT) modified glassy carbon (GC) electrode. Bare GC electrode fails to determine the concentration of FA in the presence of AA and UA due to the surface fouling caused by the oxidized products of AA and FA. However, the p-AMT film modified electrode not only separates the voltammetric signals of AA, UA and FA with potential differences of 170 and 410 mV between AA–UA and UA–FA, respectively but also shows higher oxidation current for these analytes. The p-AMT film modified electrode displays an excellent selectivity towards the determination of FA even in the presence of 200-fold AA and 100-fold UA. Using amperometric method, we achieved the lowest detection of 75 nM UA and 100 nM each AA and FA. The amperometric current response was increased linearly with increasing FA concentration in the range of 1.0 × 10⁻⁷–8.0 × 10⁻⁴ M and the detection limit was found to be 2.3 × 10⁻¹⁰ M (S/N = 3). The practical application of the present modified electrode was successfully demonstrated by determining the concentration of FA in human blood serum samples.     

Determination of ascorbic acid by polypyrrole potentiometric detector in ion chromatography

A potentiometric detector, based on electrodeposition of polypyrrole onto Pt electrode, was investigated in this study. The chromatographic performance of the PPy detector was investigated in ion chromatography. The resulting PPy detector exhibited good performance for AA determination with a wide linear range (1.0 × 10⁻⁶ to 1.0 × 10⁻² M), a highly reproducible response (R.S.D. of 2.45%), without any interference and long-term stability. The calculated detection limit was 7.0 × 10⁻⁵ mM at 3σ. The calibration results showed good Nernstian behavior and also satisfactory low detection limit. In order to verify the reliability of the PPy detector, it was applied to the determination of AA in pharmaceutical samples. The results were satisfactory and agreed closely with the manufacturers’ stated contents. The PPy electrode can be used as an alternative novel potentiometric detector material for determination of AA in standards and pharmaceutical samples.     

Inhibition of prostagland in E2-induced cyclic AMP accumulation in the rat anterior pituitary by II-deoxyprostaglandin E analogs (9-ketoprostynoic acids)

The effects of various II-deoxyprostaglandin E analogs on the basal and prostaglandin E₂ (PGE₂)-induced cyclic AMP accumulation in the rat anterior pituitary were studied in vitro. 13-Hydroxy-9-oxoprost-14-ynoic acid at 5 × 10⁻⁴M, but not 5 × 10⁻⁵M, decreased (45%) the induced accumulation and did not alter the basal accumulation; 15-hydroxy-9-oxoprost-13-ynoic acid at 5 × 10⁻⁴M caused less of a decrease (29%) in the induced and also did not alter the basal accumulation. (14Z)-13-Hydroxy-9-oxoprost-14-enoic acid at 5 × 10⁻⁴M did not alter the induced and caused a slight increase (5 fold) in the basal accumulation. 7-Oxa-13-prostynoic acid increased slightly the basal accumulation at 5 × 10⁻⁵M (2 fold) and 2.33 × 10⁻⁴M (6 fold) and did not antagonize the induced accumulation. Thus, the 9-ketoprostynoic acids are effective PGE₂ antagonists in this system.     

Inhibition of prostaglandin E2-induced cyclic AMP accumulation in the rat anterior pituitary by 11-deoxyprostaglandin E analogs (9-ketoprostynoic acids)

The effects of various 11-deoxyprostaglandin E analogs on the basal and prostaglandin E₂ (PGE₂)-induced cyclic AMP accumulation in the rat anterior pitutiary were studied . 13-Hydroxy-9-oxoprost-14-ynoic acid at 5 × 10⁻⁴M, but not 5 × 10⁻⁵M, decreased (45%) the induced accumulation and did not alter the basal accumulation; 15-hydroxy-9-oxoprost-13-ynoic acid at 5 × 10⁻⁴M caused less of a decrease (29%) in the induced and also did not alter the basal accumulation. (14Z)-13-Hydroxy-9-oxoprost-14-enoic acid at 5 × 10⁻⁴M did not alter the induced and caused a slight increase (5 fold) in the basal accumulation. 7-Oxa-13-prostynoic acid increased slightly the basal accumulation at 5 × 10⁻⁵M (2 fold) and 2.33 × 10⁻⁴M (6 fold) and did not antagonize the induced accumulation. Thus, the 9-ketoprostynoic acids are effective PGE₂ antagonists in this system.     

A sugar-aza-crown ether-based fluorescent sensor for Hg and Cu

A fluorescent sensor, 5, based upon the sugar-aza-crown ether structure with two anthracenetriazolymethyl groups was prepared and its fluoroionophoric properties toward transition metal ions were investigated. In methanol, the sensor exhibits highly selective recognition of Cu²⁺ and Hg²⁺ ions among a series of tested metal ions. The association constant for 5·Cu²⁺ and 5·Hg²⁺ in methanol was calculated to be 4.0 × 10⁵ M⁻¹ and 1.1 × 10⁵ M⁻¹, respectively. The detection limits for the sensing of Cu²⁺ and Hg²⁺ ions were 1.39 × 10⁻⁶ M and 1.39 × 10⁻⁵ M, respectively.     

Effect of prostaglandin F2α on propulsive activity of the isolated segmental colon of the guinea-pig

The effects of prostaglandin F_2α (PGF_2α) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated.Using experimental conditions under which spontaneous propulsive activity was negligible, PGF_2α (5×10⁻⁸×1×10⁻⁶M), added to the bathing medium, increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1×10⁻⁷g/ml).The contractions produced by PGF_2α(5×10⁻⁷ − 1×10⁻⁵M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1×10⁻⁷ g/ml).From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF_2α may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.