A major challenge in the development of bioanalytical methods is to achieve a rapid and robust quantification of disease biomarkers present at very low concentration levels in complex biological samples. An immunoassay platform is presented herein for ultrasensitive and fast detection of the prostate-specific antigen (PSA), a well-recognized cancer biomarker. A sandwich type immunosensor has been developed employing a detection antibody labeled with inorganic nanoparticles acting as tags for further indirect quantification of the analyte. The required high sensitivity is then achieved through a controlled gold deposition on the nanoparticle surface, carried out after completing the recognition step of the immunoassay, thus effectively amplifying the size of the nanoparticles from nm to µm range. Due to such an amplification procedure, quantification of the biomolecule could be carried out directly on the immunoassay plates using confocal microscopy for measurement of the reflected light produced by gold-enlarged nanostructures. The high specificity of the immunoassay was demonstrated with the addition of a major abundant protein in serum (albumin) at much higher concentrations. An extremely low detection limit for PSA quantification (LOD of 1.1 fg·mL⁻¹ PSA) has been achieved. Such excellent LOD is 2–3 orders of magnitude lower than the clinically relevant PSA levels present in biological samples (4–10 ng·mL⁻¹) and even to monitor eventual recurrence after clinical treatment of a prostate tumor (0.1 ng·mL⁻¹). In fact, the broad dynamic range obtained (4 orders of magnitude) would allow the PSA quantification of diverse samples at very different relevant levels.

中文翻译：

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前列腺特异性抗原超灵敏光学免疫传感的催化金沉积。

生物分析方法发展中的主要挑战是对复杂生物样品中浓度很低的疾病生物标志物进行快速，可靠的定量分析。本文提供了一种免疫测定平台，用于超灵敏和快速检测前列腺特异性抗原（PSA），一种公认的癌症生物标记物。已经开发出一种夹心型免疫传感器，其采用被无机纳米颗粒标记的检测抗体作为进一步间接定量分析物的标签。然后，通过在完成免疫测定的识别步骤之后在纳米粒子表面进行可控的金沉积，从而实现所需的高灵敏度，从而有效地将纳米粒子的尺寸从nm扩大到µm范围。由于这种放大程序，可以使用共聚焦显微镜直接在免疫测定板上对生物分子进行定量，以测量由金放大的纳米结构产生的反射光。通过在血清中添加大量丰富的主要蛋白质（白蛋白）证明了免疫测定的高特异性。PSA定量的检测限极低（LOD为1.1 fg·mL达到^-1 PSA）。这样优异的LOD是2-3个数量级比临床相关生物样品中存在的PSA水平降低（4-10纳克·ML ^-1），甚至临床治疗前列腺肿瘤的（0.1纳克后监测最终复发·毫升^{- 1}）。实际上，所获得的宽动态范围（4个数量级）将使PSA定量分析不同样品的相关水平。