Early diagnosis and clinical treatments of breast cancer provide a highly successful chance for patients to survive. Herein, the detection of CA 27-29 breast cancer antigen was conducted using a label-free ultrasensitive electrochemical immunosensor Au/MoS₂/rGO nanocomposite system. The high electrochemical sensitivity of the as-prepared nanocomposites was provided as a result of the high synergistic effect between AuNPs, MoS₂ and rGO. Signal amplification of the amperometric detection was evaluated by monitoring the electrocatalytic current response of hydrogen peroxide reduction through the immunoreaction between the anti-CA 27-29 and CA 27-29 antigen on the surface of the Au/MoS₂/rGO nanocomposites. The immunosensor displayed an excellent specificity and high sensitivity towards the detection of CA 27-29 breast cancer antigen in human serum with low detection limits of 0.08 U mL⁻¹. The reproducibility, stability and specificity of the suggested immunosensor were evaluated and the recorded results indicated that this type of immunosensor can play an important role in the clinical diagnosis of different types of tumor markers.

A label-free ultrasensitive electrochemical immunosensor has been designed for the detection of calcitonin, a medullary thyroid carcinoma tumor marker. The immunosensor was fabricated by deposition of gold nanoparticles and graphene oxide on the activated surface of a glassy carbon electrode. The incorporation of the nanocomposite leads to the increased surface area of the immunosensor, which translates into an enhanced sensitivity. The modified surface of the immunosensor improves the loading of anti-calcitonin capture antibody. Furthermore, the gold nanoparticles and graphene oxide nanocomposite are coupled with the sensor surface through aryldiazonium salts via covalent bonds, which stabilizes the sensing interface. The anti-calcitonin detection antibodies are immobilized on the sensor surface that is modified using ferrocene-graphene oxide molecules for detecting calcitonin level. The signal of the modified sensor is determined based on the shift of peak current, which is a consequence of the change in surface charge due to the antigen–antibody sandwich-type immunoreaction. Under optimized conditions, the output peak current shift was directly proportional to the calcitonin concentration, with a dynamic linearity range from 0.001 to 1.0 ng mL⁻¹ and a detection limit as low as 0.7 pg mL⁻¹. The designed immunosensor exhibited an acceptable selectivity for the detection of human calcitonin with a high sensitivity at low concentrations.

A chemiluminescence (CL) method using flow injection (FI) has been investigated for the rapid and sensitive determination of enalapril maleate. The method is based on the CL reaction of the drug with tris(2,2′-bipyridyl)ruthenium(II), Ru(bipy)32+ and acidic potassium permanganate. After selecting the best operating parameters, calibration graphs were obtained over concentration ranges of 0.005 - 0.2 μg/ml and 0.7 - 100 μg/ml with a detection limit (S/N = 2) of 1.0 ng/ml. The average % found was 99.9 ± 0.7 and 100.2 ± 0.3 for the two concentration ranges respectively. %RSD (n = 10) for 5.0 μg/ml was 0.44. The method was successfully applied to the determination of enalapril maleate in dosage forms and biological fluids without interferences.

The present study suggested six different fluorimetric systems for the determination of three angiotensin II receptor antagonists, candesartan cilexetil (CDC), valsartan (VAL) and telmisartan (TEL) in their bulk and pharmaceutical dosage forms. The fluorescence intensities (FIs) were recorded by measuring the high catalytic potential activity of silver or gold nanoparticles (AgNPs or AuNPs) at λ_ex 525, 420 and 330 nm and λ_em 555, 490 and 400 nm for CDC, VAL and TEL, respectively. All experimental measurements were carried out under optimum conditions using the CDC–Tb(III)–AgNPs, CDC–Tb(III)–AuNPs, VAL–Eu(III)–AgNPs, VAL–Eu(III)–AuNPs, TEL–SDS–AgNPs and TEL–SDS–AuNPs systems. The fluorescence (FL) signals displayed linear concentration ranges of 0.01–300, 0.02–120 and 2.0–30 ng mL⁻¹ for CDC, VAL and TEL in the presence of AgNPs, respectively, and 0.05–60, 0.1–80 and 0.1–250 ng mL⁻¹ for the same drugs in the presence of AuNPs, respectively. The influence of possible coexisting species and additives was tested. ICH guidelines were followed to validate the developed methods. All suggested FL systems were successfully used to monitor the investigated drugs in bulk, tablets and bio-samples. The obtained data were compared with those of other reported methods revealing high agreement.