Utility of slot-blot-ELISA as a new, fast, and sensitive immunoassay for detection of carcinoembryonic antigen in the urine samples of patients with various gastrointestinal malignancies

Enzyme-Linked Immunosorbent Assay: Types and Applications

Enzyme-linked immunosorbent assay (ELISA) is an immunological assay widely used in basic science research, clinical application studies, and diagnostics. The ELISA technique relies on the interaction between the antigen (i.e., the target protein) versus the primary antibody against the antigen of interest. The presence of the antigen is confirmed through the enzyme-linked antibody catalysis of the added substrate, the products of which are either qualitatively detected by visual inspection or quantitatively using readouts from either a luminometer or a spectrophotometer. ELISA techniques are broadly classified into direct, indirect, sandwich, and competitive ELISA-all of which vary based on the antigens, antibodies, substrates, and experimental conditions. Direct ELISA relies on the binding of the enzyme-conjugated primary antibodies to the antigen-coated plates. Indirect ELISA introduces enzyme-linked secondary antibodies specific to the primary antibodies bound to the antigen-coated plates. Competitive ELISA involves a competition between the sample antigen and the plate-coated antigen for the primary antibody, followed by the binding of enzyme-linked secondary antibodies. Sandwich ELISA technique includes a sample antigen introduced to the antibody-precoated plate, followed by sequential binding of detection and enzyme-linked secondary antibodies to the recognition sites on the antigen. This review describes ELISA methodology, the types of ELISA, their advantages and disadvantages, and a listing of some multifaceted applications both in clinical and research settings, including screening for drug use, pregnancy testing, diagnosing disease, detecting biomarkers, blood typing, and detecting SARS-CoV-2 that causes coronavirus disease 2019 (COVID-19).

Current status of urinary diagnostic biomarkers for colorectal cancer

Fecal occult blood test (FOBT) and flexible sigmoidoscopy are the currently using screening methods for colorectal cancer (CRC). However, these methods still have problems of high false positive rates in FOBT and increased invasiveness and cost associated with endoscopy. The development of non-invasive biomarkers is thus important for the diagnosis of CRC. Urine is one of the most commonly used samples for mass screening owing to its non-invasive and simple process of collection; however, the discovery of urinary diagnostic biomarkers for malignancies is still challenging and developing. Since urine contains abundant substances reflecting systemic body condition, urinary biomarker might contribute to detect CRC in a completely non-invasive manner. In this review, we describe the current utility of urinary diagnostic biomarkers for CRC.

An ultrasensitive homogeneous aptasensor for carcinoembryonic antigen based on upconversion fluorescence resonance energy transfer

Carcinoembryonic antigen (CEA) has been recognized as one of the most important tumor markers. Herein, we reported an ultrasensitive homogeneous aptasensor based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and graphene oxide (GO) for CEA detection. The CEA aptamer modified UCNPs can bind to the surface of GO through π-π stacking interaction, resulting in fluorescence quenching due to the energy transfer from UCNPs to GO. After the introduction of CEA, the CEA aptamer preferentially combined with CEA to form three-dimensional structure which made UCNPs-aptamer dissociate from the GO, blocking the energy transfer process. The fluorescence of UCNPs was accordingly restored in a CEA concentration-dependent manner both aqueous solution and human serum samples. The aptasensor could monitor CEA level directly in human serum and the results were strongly correlated with commercial chemiluminescence kits. The excellent detection performance suggested promising prospect of the aptasensor in practical application.

Role of Urinary Biomarkers in the Diagnosis of Adenoma and Colorectal Cancer: A Systematic Review and Meta-Analysis

The growing interest in enhancing and spreading colorectal cancer (CRC) screening has been stimulating the exploration of novel biomarkers with greater sensitivity and specificity than immunochemical faecal occult blood test (iFOBT). The present study provides i) a systematic review of the urinary biomarkers that have been tested to achieve early CRC diagnosis and assess the risk of colorectal adenoma and adenocarcinoma, and ii) a meta-analysis of the data regarding the urinary prostaglandin (PG) metabolite PGE-M. As regard to gene markers, we found significantly different percent methylation of the vimentin gene in CRC patients and healthy controls (HC) (p<0.0001). Respect to metabolism of nitrogenous bases, cytidine, 1-methyladenosine, and adenosine, have higher concentrations in CRC patients than in HC (respectively, p<0.01, p=0.01, and p<0.01). As regard to spermine we found that N1,N12 diacetyl spermine (DiAcSpm) and N1, N8 diacetylspermidine (DiAcSpd) were significantly higher in CRC than in HC (respectively p=0.01 and p<0.01). Respect to PGE-M, levels were higher in CRC than in those with multiple polyposis (p<0.006) and HC subjects (p<0.0004). PGE-M seems to be the most interesting and promising urinary marker for CRC and adenoma risk assessment and for CRC screening. In conclusion, evidence suggests that urinary biomarker could have a potential role as urinary biomarkers in the diagnosis of colorectal cancer. Particularly, PGE-M seems to be the most promising urinary marker for CRC early detection.

Fluorescence resonance energy transfer biosensor between upconverting nanoparticles and palladium nanoparticles for ultrasensitive CEA detection

An ultrasensitive biosensor for carcinoembryonic antigen (CEA) was constructed based on fluorescence resonance energy transfer (FRET) between upconverting nanoparticles (UCPs) and palladium nanoparticles (PdNPs). PdNPs was synthesized by the addition of a solution of Na2PdCl4 into a mixture of N2H4·H2O as the reducing agent and 11-mercaptoundecanoic acid (MUDA) as the stabilizer. The CEA aptamer (5'-NH2-ATACCAGCTTATTCAATT-3') was conjugated to hexanedioic acid (HDA) modified UCPs (HDA-UCPs) through an EDC-NHS coupling protocol. The coordination interaction between nitrogen functional groups of the CEA aptamer and PdNPs brought UCPs and PdNPs in close proximity, which resulted in the fluorescence quenching of UCPs to an extent of 85%. And the non-specific fluorescence quenching caused by PdNPs towards HDA-UCPs was negligible. After the introduction of CEA into the UCPs-CEA aptamer-PdNPs fluorescence quenching system, the CEA aptamer preferentially combined with CEA accompanied by the conformational change which weakened the coordination interaction between the CEA aptamer and PdNPs. So fluorescence recovery of UCPs was observed and a linear relationship between the fluorescence recovery of UCPs and the concentration of CEA was obtained in the range from 2pg/mL to 100pg/mL in the aqueous buffer with the detection limit of 0.8pg/mL. The ultrasensitive detection of CEA was also realized in diluted human serum with a linear range from 4pg/mL to 100pg/mL and a detection limit of 1.7pg/mL. This biosensor makes the most of the high quenching ability of PdNPs towards UCPs with negligible non-specific fluorescence quenching and has broad application prospects in biochemistry.

Urinary protein biomarkers of cancer

BACKGROUND

Although several cancer biomarkers are now in use, few have the necessary sensitivity and specificity to eliminate the need for invasive diagnostic procedures. With the expansion of proteomics, new technologies have been used to study various cancers, resulting in the discovery of several potential urine biomarkers. Urine is an ideal medium for the detection of biomarkers because of the non-invasive means of collecting samples and demonstrated shedding of cells, proteins, enzymes, nucleic acids and metabolic products into urine during various pathological processes.

OBJECTIVE

To review the contemporary literature regarding urinary protein markers of cancer.

METHODS

A PubMed search for 'urinary protein biomarkers of cancer' revealed 4679 scientific publications. The search was limited to studies published over the last 5 years and reviewed pertinent findings regarding biomarker evaluation and discovery.

RESULTS

Several urinary protein biomarkers have been described for urologic, gynecologic, gastrointestinal and neurologic tumors. Some have been selected for use in clinical practice, whereas others have been abandoned owing to inconclusive follow-up studies.

CONCLUSION

Several potential urinary protein markers for cancer exist, yet multi-institutional, prospective trials are needed to validate results before implementation in clinical scenarios.